knights tour using a stack - c++

I'm tasked with solving the Knights tour iteratively using a stack to store the previous moves so I can pop if the knight is stuck. My program seems to be making multiple POPS but doesn't seem to be ever solving the puzzle.
It uses Warnsdorffs rule for the first 32 moves and then uses a stack to solve the remaining spaces.
Is there something wrong with my logic so that it never solves the puzzle?
Is this a legal move function
bool safe(int row, int col) {
if (row >= 0 && row < 8 && col >= 0 && col < 8 && arr[row][col] == -1){
return true;
}
return false;
}// end safe
Here is the solve function
void solve(){
int x = 0; // initial start
int y = 0; // initial start
arr[0][0] = 0; // loading array with starting position
int nextMoveX, nextMoveY; // next move
Location top;
top.x = 0;
top.y = 0;
for(int i = 0; i < 8; i++){
top.movesArray[i] = safe(top.x+moveX[i], top.y+moveY[i]);
}
locate.push(top); // loading stack with initial position
int bestMove[8]; // array to sort best move
int counter = 0; // move counter
int count = 0;
while(counter < 63){
top = locate.top(); // check top of stack for current position
x = top.x;
y = top.y;
//loops through the 8 move choices
// using a stack to solve final steps
if( counter >= 31){
for(int i = 0; i < 8; i++){
top = locate.top();
if(top.movesArray[i]){
if(counter == 42){
cout << i;
}
//updates the top of the stack removing the
move just made from being made on a POP
top.movesArray[i] = false;
locate.pop();
locate.push(top);
counter++;
nextMoveX = x + moveX[i];
nextMoveY = y + moveY[i];
arr[nextMoveX][nextMoveY] = counter;
top.x = nextMoveX;
top.y = nextMoveY;
print();
cout << counter;
for(int j = 0; j < 8; j++){
top.movesArray[j] = safe(nextMoveX+moveX[j], nextMoveY+moveY[j]);
cout << top.movesArray[j];
}
locate.push(top);
break;
}
//if no more valid moves from this space pop off
if(i == 7){
arr[top.x][top.y]= -1;
locate.pop();
counter --;
cout << "pop";
top = locate.top();
for(int a = 0; a < 8; a++){
cout << top.movesArray[a];
}
break;
}
}
}
// heuristics for first 32 moves
else{
for(int i = 0; i < 8; i++){
bestMove[i] = -1; // resets # of potential moves at next space
print();
// test next position
nextMoveX = x + moveX[i];
nextMoveY = y + moveY[i];
//if safe count number of moves on next space
if(safe(nextMoveX,nextMoveY)){
for( int j = 0; j < 8; j++){
if(safe(nextMoveX+moveX[j],nextMoveY+moveY[j])){
bestMove[i] += 1;
}
}
}
//if on last move check for one with least moves available
if(i ==7){
int least = 8;
int pos = -1;
int L;
for(L = 0; L < 8; L++){
if(bestMove[L] < least && bestMove[L] != -1 && bestMove[L]!= 0){
least = bestMove[L];
pos = L;
}
} // end for
counter++;
nextMoveX = x + moveX[pos];
nextMoveY = y + moveY[pos];
arr[nextMoveX][nextMoveY] = counter;
top.x = nextMoveX;
top.y = nextMoveY;
for(int e = 0; e < 8; e++){
top.movesArray[e] = safe(nextMoveX + moveX[e],nextMoveY + moveY[e]);
}
locate.push(top);
} // end if (i=7)
} // end for i
} // end else
} // end while
} // end solve


It is probably a SIGSEGV (segmentation fault) because you are trying to write past the size of arr.
How is arr declared? Do you make sure that when you do this:
arr[nextMoveX][nextMoveY] = counter;
nextMoveX and nextMoveY are within the array dimension values as declared(or malloc'd)?

Related

N Queen using C++ with Dynamic 2D Array

I have been having difficulty solving the N Queen problem, I am able to implement most of my functions, but the function that places the Queen recursively with backtracking. The placeQueens function is using a provided pseudocode that is required for the project. I had to create the array on the heap that is pointing to boardPtr, which is also required. I have a while loop condition that I have but I am not sure if it's correct. I have tried looking online for similar code but none of them were able to help me.
Here is my code:
#include <iostream>
#include "ChessBoard.h"
int main()
{
// Create a board
ChessBoard myBoard;
/* Loop through board sizes from 3 to 13.
Since 3 and 13 are invalid you should see
board sizes 4 and 12 twice. */
for (int i = 3; i <= 13; i++)
{
myBoard.setSize(i);
/* Attempt to solve the N-Queens Problem. If the solve
code is working it should find solutions for all
sizes. */
if (!myBoard.solve())
std::cout << "Sorry, no solution was found for board size "
<< myBoard.getSize() << "." << std::endl << std::endl;
else
{
std::cout << "Size " << myBoard.getSize()
<< " solution:" << std::endl;
myBoard.displayBoard();
std::cout << std::endl << std::endl;
}
}
return 0;
}
#include "ChessBoard.h"
#include <iostream>
using namespace std;
bool ChessBoard::placeQueens( int column)
{
int row = 0;
if (column >= boardSize)
{
// The board is filled, problem is solved.
return true;
}
else
{
while (row < boardSize && column < boardSize) // unconsidered rows exist in column
{
if ((canPlace(boardPtr, row, column)) == true) //[row][column] is unattacked
{
//Place a queen in the un - attacked square.
boardPtr[row][column] = 'Q';
//Do a recursive call to try and place queens in subsequent columns :
if (!placeQueens(column + 1))
{
//If we’re here, placement of the last queen resulted in a dead end; no solution could be found.Remove the last queen placed.
boardPtr[row][column] = '*';
//Move to next row so search can continue in next iteration.
row++;
}
else
{
// If we’re here, recursive calls were able to place queens in all columns to the right of column, the problem is solved.
return true;
}
}
else
{
//Square is attacked, move to next row.
row++;
}
}
//All rows have been considered in column without a successful queen placement.Backtrack by returning false.
return false;
}
}
bool ChessBoard::canPlace(char** boardPtr, int row, int column)
{
int i, j;
// Check row
for (i = 0; i < column; i++)
if (boardPtr[row][i] )
return false;
// Check upper diagonal
for (i = row, j = column; i >= 0 && j >= 0; i--, j--)
if (boardPtr[i][j])
return false;
// Check lower diagonal
for (i = row, j = column; j >= 0 && i < boardSize; i++, j--)
if (boardPtr[i][j] )
return false;
return true;
}
ChessBoard::ChessBoard()
{
boardSize = 8;
boardPtr = nullptr;
}
ChessBoard::ChessBoard(int size)
{
if (size < 4)
{
boardSize = 4;
}
else if (size > 12)
{
boardSize = 12;
}
}
ChessBoard::~ChessBoard()
{
}
int ChessBoard::setSize(int size)
{
delete[] boardPtr;
//Initialize array at size 4
if (size < 4)
{
boardSize = 4;
char** chessBoard = new char* [4];
for (int i = 0; i < 4; i++)
{
chessBoard[i] = new char[4];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
//Initialize array at size 12
else if (size > 12)
{
boardSize = 12;
char** chessBoard = new char* [12];
for (int i = 0; i < size; i++)
{
chessBoard[i] = new char[12];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
//Initialize array at given size
else
{
boardSize = size;
char** chessBoard = new char* [size];
for (int i = 0; i < size; i++)
{
chessBoard[i] = new char[size];
}
// Point initialized ChessBoard to boardPtr
boardPtr = chessBoard;
// Fill ChessBoard with *
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
boardPtr[i][j] = '*';
}
}
}
return 1;
}
int ChessBoard::getSize()
{
return boardSize;
}
bool ChessBoard::solve()
{
int column = 0;
if (placeQueens(column) == false)
{
return false;
}
else
{
return true;
}
}
void ChessBoard::displayBoard()
{
for (int i = 0; i < boardSize; i++)
{
for (int j = 0; j < boardSize; j++)
{
cout << boardPtr[i][j] << " ";
}
cout << endl;
}
}
#ifndef CHESSBOARD_H
#define CHESSBOARD_H
class ChessBoard
{
private:
char** boardPtr;
int boardSize;
bool placeQueens( int column);
bool canPlace(char** boardPtr, int row, int col);
public:
ChessBoard();
ChessBoard(int size);
~ChessBoard();
int setSize(int size);
int getSize();
bool solve();
void displayBoard();
};
#endif

Interesting task you have! I decided to implement my own code from scratch for solving N Queen problem. Actually I implemented it for any board size N, not just equal to 8.
I didn't fix bugs in your code, but instead implemented my own solution. Although it may be not the answer you want, still it would be a good thing from educational point of view. Hoping that there would be other answers later that are fixing bugs in your code, as you wished.
I made code very optimized, so it is not very simple from first side, but solves task very fast, using BackTracking, with several extra techniques of speeding it up.
After program finishes it prints to console all solutions in a nice form. Please scroll down below the code to see example of console output.
First program has some extra descriptive comments to show what's happenning in program.
Notice that I provided two codes below, first is simplified version, that is more easy to understand, so it is better from educational point of view. Second code is advanced one, it is more difficult, but solves task fast. Please look at first code if you want just to learn basics, and look at second code if you want to learn advanced techniques.
Simplified:
Try it online!
#include <iostream>
#include <vector>
#include <string>
void Output(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines, bool last);
void Solve(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines,
int N, int & num_sol, int cnt = 0, int start_i = 0, int start_j = 0, int depth = 0) {
if (cnt >= N) {
Output(board, lines, false);
// Increase number of solutions.
++num_sol;
return;
}
// Traverse whole board starting from last queen
for (int i = start_i; i < board.size(); ++i)
for (int j = i == start_i ? start_j : 0; j < board[i].size(); ++j) {
bool attacked = false;
// k-loop checks if position [i][j] is being attacked
for (int k = 0; k < (board.size() > board[i].size() ?
board.size() : board[i].size()); ++k)
if (
// Is there horizontal attack
k < board[i].size() && k != j && board[i][k] ||
// Is there vertical attack
k < board.size() && k != i && board[k][j] ||
// Is there main diagonal attack
k < board.size() && k != i && 0 <= j - i + k &&
j - i + k < board[i].size() && board[k][j - i + k] ||
// Is there secondary diagonal attack
k < board.size() && k != i && 0 <= j + i - k &&
j + i - k < board[i].size() && board[k][j + i - k]
) {
attacked = true;
break;
}
if (attacked)
continue;
// Position [i][j] is not under attack, hence placing a queen
board[i][j] = true;
// Recursive descend to place another queen
Solve(board, lines, N, num_sol, cnt + 1, i, j + 1, depth + 1);
// Backtrack, to delete previous queen
board[i][j] = false;
}
if (depth == 0)
Output(board, lines, true);
}
// Function of outputting solutions to console
void Output(std::vector<std::vector<bool>> & board, std::vector<std::string> & lines, bool last) {
if (1) {
if (!last) {
for (int i = 0; i < board.size(); ++i) {
for (int j = 0; j < board[i].size(); ++j)
lines[i].push_back(board[i][j] ? 'Q' : '.');
lines[i] += "|";
}
}
if (lines.at(0).size() >= 70 || last && !lines.at(0).empty()) {
for (int i = 0; i < lines.size(); ++i)
std::cout << lines[i] << std::endl;
for (int j = 0; j < lines.at(0).size(); ++j)
std::cout << (lines.at(0)[j] == '|' ? '+' : '-');
std::cout << std::endl;
lines.clear();
lines.resize(board.size());
}
}
}
int main() {
// rows - number of rows in a board, cols - number of columns in a board
// N - number of queens to be placed
int const rows = 8, cols = 8, N = 8;
// Filling with empty values board [rows][cols]
std::vector<std::vector<bool>> board(rows, std::vector<bool>(cols));
std::vector<std::string> lines(rows);
// Answer, number of solutions
int num_sol = 0;
// Starting a backtracking
Solve(board, lines, N, num_sol);
// Outputting answer
std::cout << "Number of solutions: " << num_sol << std::endl;
}
Advanced:
Try it online!
#include <iostream>
#include <string>
#define MAX(a, b) ((a) >= (b) ? (a) : (b))
enum { max_rows = 32, max_cols = 32, max_max_rows_cols = MAX(max_rows, max_cols) };
void Output(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
int rows, int cols, bool last);
void Solve(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
bool (& busy_cols)[max_cols], bool (& busy_diagA)[2 * max_max_rows_cols],
bool (& busy_diagB)[2 * max_max_rows_cols],
int rows, int cols, int N, int & num_sol, int cnt = 0, int start_i = 0, int depth = 0) {
if (cnt >= N) {
Output(board, lines, rows, cols, false);
++num_sol;
return;
}
int const max_rows_cols = MAX(rows, cols);
if (rows - start_i < N - cnt)
return;
int avail_cols[max_cols];
int avail_cols_cnt = 0;
for (int j = 0; j < cols; ++j)
if (!busy_cols[j]) {
avail_cols[avail_cols_cnt] = j;
++avail_cols_cnt;
}
if (avail_cols_cnt < N - cnt)
return;
for (int i = start_i; i < rows; ++i)
for (int jj = 0; jj < avail_cols_cnt; ++jj) {
int const j = avail_cols[jj];
if (busy_diagA[max_rows_cols + j - i] || busy_diagB[j + i])
continue;
board[i][j] = true;
busy_cols[j] = true;
busy_diagA[max_rows_cols + j - i] = true;
busy_diagB[j + i] = true;
Solve(board, lines, busy_cols, busy_diagA, busy_diagB,
rows, cols, N, num_sol, cnt + 1, i + 1, depth + 1);
board[i][j] = false;
busy_cols[j] = false;
busy_diagA[max_rows_cols + j - i] = false;
busy_diagB[j + i] = false;
}
if (depth == 0)
Output(board, lines, rows, cols, true);
}
void Output(bool (& board)[max_rows][max_cols], std::string (& lines)[max_rows],
int rows, int cols, bool last) {
if (1) {
if (!last) {
for (int i = 0; i < rows; ++i) {
for (int j = 0; j < cols; ++j)
lines[i].push_back(board[i][j] ? 'Q' : '.');
lines[i] += "|";
}
}
if (lines[0].size() >= 70 || last && !lines[0].empty()) {
for (int i = 0; i < rows; ++i)
std::cout << lines[i] << std::endl;
for (int j = 0; j < lines[0].size(); ++j)
std::cout << (lines[0][j] == '|' ? '+' : '-');
std::cout << std::endl;
for (int i = 0; i < rows; ++i)
lines[i].clear();
}
}
}
int main() {
int const rows = 8, cols = 8, N = 8;
bool board[max_rows][max_cols] = {};
std::string lines[max_rows] = {};
bool busy_cols[max_cols] = {};
bool busy_diagA[2 * max_max_rows_cols] = {};
bool busy_diagB[2 * max_max_rows_cols] = {};
int num_sol = 0;
Solve(board, lines, busy_cols, busy_diagA, busy_diagB, rows, cols, N, num_sol);
std::cout << "Number of solutions: " << num_sol << std::endl;
}
Output:
Q.......|Q.......|Q.......|Q.......|.Q......|.Q......|.Q......|.Q......|
....Q...|.....Q..|......Q.|......Q.|...Q....|....Q...|....Q...|.....Q..|
.......Q|.......Q|...Q....|....Q...|.....Q..|......Q.|......Q.|Q.......|
.....Q..|..Q.....|.....Q..|.......Q|.......Q|Q.......|...Q....|......Q.|
..Q.....|......Q.|.......Q|.Q......|..Q.....|..Q.....|Q.......|...Q....|
......Q.|...Q....|.Q......|...Q....|Q.......|.......Q|.......Q|.......Q|
.Q......|.Q......|....Q...|.....Q..|......Q.|.....Q..|.....Q..|..Q.....|
...Q....|....Q...|..Q.....|..Q.....|....Q...|...Q....|..Q.....|....Q...|
--------+--------+--------+--------+--------+--------+--------+--------+
.Q......|.Q......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|..Q.....|
.....Q..|......Q.|......Q.|.......Q|Q.......|....Q...|....Q...|....Q...|
.......Q|..Q.....|....Q...|.....Q..|......Q.|.Q......|.Q......|......Q.|
..Q.....|.....Q..|.......Q|Q.......|....Q...|.......Q|.......Q|Q.......|
Q.......|.......Q|Q.......|..Q.....|.......Q|Q.......|.....Q..|...Q....|
...Q....|....Q...|...Q....|....Q...|.Q......|......Q.|...Q....|.Q......|
......Q.|Q.......|.....Q..|......Q.|...Q....|...Q....|......Q.|.......Q|
....Q...|...Q....|..Q.....|...Q....|.....Q..|.....Q..|Q.......|.....Q..|
--------+--------+--------+--------+--------+--------+--------+--------+
..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|
....Q...|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
.......Q|.Q......|.Q......|.Q......|...Q....|...Q....|.......Q|.......Q|
...Q....|....Q...|......Q.|......Q.|Q.......|.Q......|Q.......|Q.......|
Q.......|.......Q|Q.......|....Q...|.......Q|.......Q|...Q....|....Q...|
......Q.|Q.......|...Q....|Q.......|....Q...|....Q...|......Q.|......Q.|
.Q......|......Q.|.......Q|.......Q|......Q.|......Q.|....Q...|.Q......|
.....Q..|...Q....|....Q...|...Q....|.Q......|Q.......|.Q......|...Q....|
--------+--------+--------+--------+--------+--------+--------+--------+
..Q.....|..Q.....|..Q.....|..Q.....|...Q....|...Q....|...Q....|...Q....|
.....Q..|......Q.|......Q.|.......Q|Q.......|Q.......|.Q......|.Q......|
.......Q|.Q......|.Q......|...Q....|....Q...|....Q...|....Q...|......Q.|
.Q......|.......Q|.......Q|......Q.|.......Q|.......Q|.......Q|..Q.....|
...Q....|....Q...|.....Q..|Q.......|.Q......|.....Q..|.....Q..|.....Q..|
Q.......|Q.......|...Q....|.....Q..|......Q.|..Q.....|Q.......|.......Q|
......Q.|...Q....|Q.......|.Q......|..Q.....|......Q.|..Q.....|Q.......|
....Q...|.....Q..|....Q...|....Q...|.....Q..|.Q......|......Q.|....Q...|
--------+--------+--------+--------+--------+--------+--------+--------+
...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|
.Q......|.Q......|.Q......|.Q......|.....Q..|.....Q..|.....Q..|......Q.|
......Q.|......Q.|.......Q|.......Q|Q.......|.......Q|.......Q|Q.......|
..Q.....|....Q...|....Q...|.....Q..|....Q...|.Q......|..Q.....|.......Q|
.....Q..|Q.......|......Q.|Q.......|.Q......|......Q.|Q.......|....Q...|
.......Q|.......Q|Q.......|..Q.....|.......Q|Q.......|......Q.|.Q......|
....Q...|.....Q..|..Q.....|....Q...|..Q.....|..Q.....|....Q...|.....Q..|
Q.......|..Q.....|.....Q..|......Q.|......Q.|....Q...|.Q......|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
...Q....|...Q....|...Q....|...Q....|...Q....|...Q....|....Q...|....Q...|
......Q.|......Q.|......Q.|.......Q|.......Q|.......Q|Q.......|Q.......|
..Q.....|....Q...|....Q...|Q.......|Q.......|....Q...|...Q....|.......Q|
.......Q|.Q......|..Q.....|..Q.....|....Q...|..Q.....|.....Q..|...Q....|
.Q......|.....Q..|Q.......|.....Q..|......Q.|Q.......|.......Q|.Q......|
....Q...|Q.......|.....Q..|.Q......|.Q......|......Q.|.Q......|......Q.|
Q.......|..Q.....|.......Q|......Q.|.....Q..|.Q......|......Q.|..Q.....|
.....Q..|.......Q|.Q......|....Q...|..Q.....|.....Q..|..Q.....|.....Q..|
--------+--------+--------+--------+--------+--------+--------+--------+
....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|
Q.......|.Q......|.Q......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|
.......Q|...Q....|...Q....|.....Q..|.......Q|Q.......|Q.......|.......Q|
.....Q..|.....Q..|......Q.|Q.......|Q.......|.....Q..|......Q.|...Q....|
..Q.....|.......Q|..Q.....|......Q.|...Q....|.......Q|.Q......|......Q.|
......Q.|..Q.....|.......Q|...Q....|......Q.|.Q......|.......Q|Q.......|
.Q......|Q.......|.....Q..|.......Q|..Q.....|...Q....|.....Q..|.....Q..|
...Q....|......Q.|Q.......|..Q.....|.....Q..|......Q.|...Q....|.Q......|
--------+--------+--------+--------+--------+--------+--------+--------+
....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|....Q...|
......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|.......Q|.......Q|
Q.......|Q.......|.Q......|.Q......|.Q......|...Q....|...Q....|...Q....|
..Q.....|...Q....|...Q....|.....Q..|.....Q..|Q.......|Q.......|Q.......|
.......Q|.Q......|.......Q|..Q.....|..Q.....|..Q.....|..Q.....|......Q.|
.....Q..|.......Q|Q.......|Q.......|Q.......|.......Q|.....Q..|.Q......|
...Q....|.....Q..|..Q.....|...Q....|.......Q|.....Q..|.Q......|.....Q..|
.Q......|..Q.....|.....Q..|.......Q|...Q....|.Q......|......Q.|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
Q.......|.Q......|.Q......|..Q.....|..Q.....|..Q.....|..Q.....|..Q.....|
....Q...|......Q.|......Q.|Q.......|Q.......|Q.......|....Q...|....Q...|
.Q......|Q.......|Q.......|......Q.|.......Q|.......Q|......Q.|.......Q|
.......Q|..Q.....|...Q....|....Q...|...Q....|....Q...|Q.......|Q.......|
..Q.....|....Q...|.......Q|.......Q|.Q......|.Q......|...Q....|...Q....|
......Q.|.......Q|....Q...|.Q......|......Q.|...Q....|.Q......|.Q......|
...Q....|...Q....|..Q.....|...Q....|....Q...|......Q.|.......Q|......Q.|
--------+--------+--------+--------+--------+--------+--------+--------+
.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|.....Q..|
..Q.....|..Q.....|..Q.....|...Q....|...Q....|...Q....|...Q....|.......Q|
......Q.|......Q.|......Q.|Q.......|.Q......|......Q.|......Q.|.Q......|
.Q......|.Q......|...Q....|....Q...|.......Q|Q.......|Q.......|...Q....|
...Q....|.......Q|Q.......|.......Q|....Q...|..Q.....|.......Q|Q.......|
.......Q|....Q...|.......Q|.Q......|......Q.|....Q...|.Q......|......Q.|
Q.......|Q.......|.Q......|......Q.|Q.......|.Q......|....Q...|....Q...|
....Q...|...Q....|....Q...|..Q.....|..Q.....|.......Q|..Q.....|..Q.....|
--------+--------+--------+--------+--------+--------+--------+--------+
......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|......Q.|
Q.......|.Q......|.Q......|..Q.....|..Q.....|...Q....|...Q....|....Q...|
..Q.....|...Q....|.....Q..|Q.......|.......Q|.Q......|.Q......|..Q.....|
.......Q|Q.......|..Q.....|.....Q..|.Q......|....Q...|.......Q|Q.......|
.....Q..|.......Q|Q.......|.......Q|....Q...|.......Q|.....Q..|.....Q..|
...Q....|....Q...|...Q....|....Q...|Q.......|Q.......|Q.......|.......Q|
.Q......|..Q.....|.......Q|.Q......|.....Q..|..Q.....|..Q.....|.Q......|
....Q...|.....Q..|....Q...|...Q....|...Q....|.....Q..|....Q...|...Q....|
--------+--------+--------+--------+--------+--------+--------+--------+
.......Q|.......Q|.......Q|.......Q|
.Q......|.Q......|..Q.....|...Q....|
...Q....|....Q...|Q.......|Q.......|
Q.......|..Q.....|.....Q..|..Q.....|
......Q.|Q.......|.Q......|.....Q..|
....Q...|......Q.|....Q...|.Q......|
..Q.....|...Q....|......Q.|......Q.|
.....Q..|.....Q..|...Q....|....Q...|
--------+--------+--------+--------+
Number of solutions: 92

There are several issues, starting from the multiple memory leaks (see e.g. the empty destructor or the delete[] boardPtr; at the beginning of ChessBoard::setSize), but what prevents the program to solve the problem is this:
bool ChessBoard::canPlace(char** boardPtr, int row, int column)
{
int i, j;
// Check row
for (i = 0; i < column; i++)
if (boardPtr[row][i] )
// ^^^^^^^^^^^^^^^^
return false;
// ...
}
That condition and the following ones should be boardPtr[row][i] == 'Q', because, as written, it just check if the char is not 0, while an empty spot is indicated by a . in this program.

nqueens - checking with the board, instead of previous queens

There are so many questions regarding Nqueens problem here. However, my implementation is different. My code checks with the board if queen placement is possible, instead of checking with the position of the previous queen.
It goes like this:
initially, the board has all zeros filled. The algorithm starts with the position (0,0). Then, it checks
row-wise per column to find the first 0. After finding the first zero, it changes the zero to one.
From this point onward, my logic differs. Instead of going to the next column, it first disables all the
positions, which the currently placed queen attacks, i.e. writes -1 on those places, i.e., row, column,
upper diagonal and lower diagonal. Now, the column value increments, and instead of check with the previous queen,
it simply has to find the first zero. Then again, relative positions get disabled.... you get the idea.
The code:
#include <iostream>
int board[8][8];
void printBoard() {
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
std::cout << board[i][j] << " ";
}
std::cout << "\n";
}
}
void disablePositions(int row, int col) {
//disable row
for (int j = col + 1; j < 8; j++) {
board[row][j] = 2;
}
//disable column
for (int i = 0; i < 8; i++) {
if (board[i][col] == 1) {
continue;
}
board[i][col] = 2;
}
//disable upper diagonal
for (int i = row - 1, j = col + 1; i >= 0 || j < 8; i--, j++) {
board[i][j] = 2;
}
for (int i = row + 1, j = col + 1; i < 8 || j < 8; i++, j++) {
board[i][j] = 2;
}
}
void solve(int initial_row) {
int init = initial_row;
int row = 0;
int col = 0;
while (col != 8) {
for (row = init; row < 8; row++) {
if (board[row][col] == 0) {
board[row][col] = 1;
break;
}
}
if (row == 8) {
col = 0;
initial_row++;
init = initial_row;
for (int i = 0; i < 8; i++) {
for (int j = 0; j < 8; j++) {
board[i][j] = 0;
}
}
}
else {
init = 0;
disablePositions(row, col);
col++;
}
printBoard();
std::cout << std::endl;
}
}
int main() {
solve(0);
std::cout << std::endl;
}
This code is for 8-queens. The problem is, after it reaches the stage where it starts from [5][0], it just crashes. What is causing the issue?
Also, as it tries to make an optimal choice at every stage, would we call it greedy algorithm?

In your disable upper diagonal loops, you have the condition wrong. Using an || operation, the looping continues when either condition is true, which will lead to out-of-bounds access to the array.
Change the conditions in both for loops to be && (and).

How do you find the location of a number in a sequence?

Say that I have a sequence:
int seq[4][4];
Then, lets say seq[1][2]=8;
No other values of the sequence yields 8.
If I want to find the values of a sequence and print out which one it is, (e.g. 1,2 and make x=1 and y=2) how can I do that? What

int x,j;
for (int i = 0; i < 4; i++) // looping through row
{
for(int j = 0; j < 4; j++) //looping through column
{
if (seq[i][j] == 8) //if value matches
{
x = i; y = j; //set value
i = 4; //set i to 4 to exit outer for loop
break; //exit inner for loop
}
}
}

int numberBeingSearchedFor = *Any Value Here*;
int array[*numRows*][*numColumns*];
int firstOccuranceRow = -1, firstOccuranceColumn = -1;
for(int i = 0; i < numRows; ++i)
{
for(int j = 0; j < numColumns; ++j)
{
if(array[i][j] == numberBeingSearchedFor)
{
firstOccuranceRow = i;
firstOccuranceColumn = j;
i = numRows; //Credit to other answer, I've never seen that :) It's cool
break;
}
}
}
if(firstOccuranceRow == -1 || firstOccuranceColumn == -1)
{
//Item was not in the array
}

Null characters randomly added to string C++

I have written a simple battleship game in C++. After several iterations of the game, one of the strings in a "Player" object is changed. This change is several null characters are added to the end of the string. Otherwise the rest of the object is untouched. For example if the player type is "cpu", the player type switches to "cpu\0\0\0\0\0\0\0\0". I believe the line of code causing the problem is:
currPlayer->getStrategy().getNextAttack(nextPlayer->getBoard(1));
Here is the code for getNextAttack():
int Strategy::getNextAttack(Board enemyBoard) {
//clear prob board
for(int i = 0; i < 100; i++) {
probBoard[i] = 0;
}
//reset largest ship
largestShip = 0;
//assign largest ship
for(int i = 0; i < 100; i++) {
Ship currShip = enemyBoard.getShipByCoord(i);
if(!currShip.isSunk()) { //if ship is still afloat
if(currShip.getSize() > largestShip) { largestShip = currShip.getSize(); } //reassign largest ship on board
}
}
//assign base prob
std::vector<int> allPossible;
//for all horiz coords
for(int i = 0; i < 10; i++) {
for(int j = 0; j < (10 - largestShip +1); j++) {
for(int k = 0; k < (largestShip); k++) {
if(!enemyBoard.beenHit((i*10) + j + k) || (enemyBoard.beenHit((i*10) + j + k) && !enemyBoard.getShipByCoord((i*10) + j + k).isSunk())) { //if not hit or if hit but contains a ship that is not sunk
allPossible.push_back((i*10) + j + k);
}
else {
for(int m = 0; m < k; m++) {
allPossible.pop_back(); //should delete last element
}
break;
}
}
//for all vert coords
for(int z = 0; z < (largestShip); z++) {
if(!enemyBoard.beenHit(((j+z)*10) + i)) {
allPossible.push_back(((j+z)*10) + i);
}
else {
for(int m = 0; m < z; m++) {
allPossible.pop_back(); //should delete last element
}
break;
}
}
}
}
for(int p = 0; p < allPossible.size(); p++) {
probBoard[allPossible[p]] += 1;
}
//add improvements based on hits
for(int i = 0; i < 10; i++) {
for(int k = 0; k < 10; k++) {
int currCoord = (i*10) + k;
int leftCoord = (i*10) + k-1;
int rightCoord = (i*10) + k+1;
int upCoord = ((i-1)*10) + k;
int downCoord = ((i+1)*10) + k;
if(enemyBoard.beenHit(currCoord) && (enemyBoard.getShipByCoord(currCoord).getName() != "") && !enemyBoard.getShipByCoord(currCoord).isSunk()) { //currCoord is a coordinate that has been hit, contains a ship and is not sunk
if((enemyBoard.beenHit(leftCoord) || enemyBoard.beenHit(rightCoord)) && (enemyBoard.getShipByCoord(leftCoord) == enemyBoard.getShipByCoord(currCoord) || enemyBoard.getShipByCoord(rightCoord) == enemyBoard.getShipByCoord(currCoord))) { //if space to left or right is hit and the same ship
//increment only the left and right
if(!enemyBoard.getShipByCoord(currCoord).isSunk()) { //ship cannot be sunk as well
probBoard[leftCoord] += 25;
probBoard[rightCoord] += 25;
}
}
else if((enemyBoard.beenHit(upCoord) || enemyBoard.beenHit(downCoord)) && (enemyBoard.getShipByCoord(upCoord) == enemyBoard.getShipByCoord(currCoord) || enemyBoard.getShipByCoord(downCoord) == enemyBoard.getShipByCoord(currCoord))) { //if space on top or bottom is hit and the same ship and not sunk
//increment only the top and bottom
if(!enemyBoard.getShipByCoord(currCoord).isSunk()) { //ship cannot be sunk as well
probBoard[upCoord] += 25;
probBoard[downCoord] += 25;
}
}
//if no direct spaces in any direction to hit coord, increment top, bot, left, and right equally
else {
probBoard[upCoord] += 20;
probBoard[downCoord] += 20;
probBoard[leftCoord] += 20;
probBoard[rightCoord] += 20;
}
}
}
}
//marks odds at 0 if already fired upon
for(int n = 0; n < 100; n++) {
if(enemyBoard.beenHit(n)) {
probBoard[n] = 0;
}
}
//find next best attack coord based on prob board
int highestValue = 0;
std::vector<int> highestSpaces;
for(int j = 0; j < 100; j++) {
if(probBoard[j] > highestValue) { highestValue = probBoard[j]; }
}
for(int r = 0; r < 100; r++) {
if(probBoard[r] == highestValue) {
highestSpaces.push_back(r);
}
}
srand(static_cast<unsigned int>(time(NULL)));
int randNum = rand() % highestSpaces.size();
return highestSpaces[randNum];
}
Thank you for reading and any help!

This looks like it will go out of the array bounds at the edges when the row or column is 0 or 9:
probBoard[upCoord] += 20;
probBoard[downCoord] += 20;
probBoard[leftCoord] += 20;
probBoard[rightCoord] += 20;

Puzzle related to sorting a 2-D array in ascending order

A randomly generated 4x4 2-D array is given to the user, of which one element is definitely 0. Considering 0 to be an empty location, the user will have to exchange the remaining 15 elements with 0 repeatedly until they get the array in ascending order, with 0 as the last element.
At this point, they're allowed to exchange any element with 0.
But how do I modify this code to ensure that are only able to exchange those elements with 0 that are adjacent to it (either above, below or beside it) ?
#include<iostream>
#include<stdlib.h>
#include<time.h>
using namespace std;
int check_asc(int a[][4])
{
int i, j, previous = a[0][0];
for (i = 0; i < 4; i++)
{
for (j = 0; j < 4; j++)
{
if(i == 3 && j == 3)
{
if (a[i][j] == 0)
return 1;
}
else if (a[i][j] < previous)
{
return 0;
}
previous = a[i][j];
}
}
return 1;
}
void swap(int a[][4], int &xpos, int &ypos)
{
int arr, temp;
cout << "\n\nEnter number to be swapped with 0: ";
cin >> arr;
for (int i = 0; i < 4; i++)
{
for (int j = 0; j < 4; j++)
{
if (a[i][j] == arr)
{
temp = a[xpos][ypos];
a[xpos][ypos] = a[i][j];
a[i][j] = temp;
xpos = i;
ypos = j;
return;
}
}
}
}
int check_rep(int a[][4], int assign)
{
for (int i = 0; i < 4; i++)
{
for (int j = 0; j < 4; j++)
{
if (assign == a[i][j])
return 0;
}
}
return 1;
}
void main()
{
int a[4][4], assign, xpos = 0, ypos = 0, asc_result, rep_result;
srand((unsigned)time(NULL));
for (int i = 0; i < 4; i++)
for (int j = 0; j < 4; j++)
{
if (i == 0 && j == 0)
a[i][j] = 0;
else
{
do {
assign = rand() % 50;
rep_result = check_rep(a, assign);
} while (rep_result == 0);
a[i][j] = assign;
}
}
cout << "\n\nArrange the 4x4 matrix into ascending order. (Consider 0 as a blank space)" << endl;
for (int i = 0; i < 4; i++)
{
cout << endl;
for (int j = 0; j < 4; j++)
cout << a[i][j] << '\t';
}
do {
swap(a, xpos, ypos);
system("cls");
for (int i = 0; i < 4; i++)
{
cout << endl;
for (int j = 0; j < 4; j++)
cout << a[i][j] << '\t';
}
asc_result = check_asc(a);
} while (asc_result == 0);
cout << "\n\tYou win"<<endl;
system("pause");
}

Simple, just extend your swap function with a piece of code that will check whether the location of the element to be swapped is adjacent to the location of 0:
void swap(int a[][4], int &xpos, int &ypos)
{
...
if (a[i][j] == arr &&
((i == xpos && (j == ypos - 1 || j == ypos + 1)) ||
(j == ypos && (i == xpos - 1 || i == xpos + 1))))
{
temp = a[xpos][ypos];
a[xpos][ypos] = a[i][j];
a[i][j] = temp;
xpos = i;
ypos = j;
return;
}
An improvement would be to separate the check condition and inform the user in case when the element is not adjacent to 0.

Rough Algorithm
1) create a function find location, it will return a structure Point that has x, y integer fields, it will find the x, y location of any piece based on the pieces value, i.e. lets say 0 is entered, if it is located in the top left corner (0,0), a point (0, 0) will be returned
2) create a function that takes in 2 points, the location of the '0' and the location of the piece we wish to swap lets call it S, if S.x = 0.x and 0.y - 1 = S.y or S.y - 0.y + 1 then you know that said piece is directly above or below the 0, now of course you have ot add a few conditions for boundaries so as we dont check outside the grid. Have this function return an int 1 if the piece S is located above/below/beside, 0 if not.
3) if 1 is returned your allowed to do the flip, if 0 is returned find another piece