This is my code for Project Euler #19. The answer for the problem is 171 but my code is producing 172. Please can anyone figure out the problem in the code below.
#include <bits/stdc++.h>
using namespace std ;
typedef long long LL ;
int ordYear[12] = {31,28,31,30,31,30,31,31,30,31,30,31} ;
int leapYear[12] = {31,29,31,30,31,30,31,31,30,31,30,31} ;
int main(){
int leapFlag = 0 ;
LL ans = 0 ;
int dayonfirst = 2 ; // since it was tuesday on 1 Jan 1901
for (int i=1901 ; i<=2000 ; i++){
if ( (i%4==0 && i%100!=0) || (i%100==0 && i%400==0) )
leapFlag = 1 ;
for (int i=0 ; i<12 ; i++){
int oddDays ;
if (leapFlag == 1)
oddDays = leapYear[i]%7 ;
else
oddDays = ordYear[i]%7 ;
dayonfirst += oddDays ;
if(dayonfirst == 7)
ans++ ;
else if (dayonfirst > 7)
dayonfirst = dayonfirst%7 ;
}
}
cout << ans << endl ;
return 0 ;
}
You need else statement to assign leapFlag = 0 when it not a leap year:
if ( (i%4==0 && i%100!=0) || (i%100==0 && i%400==0) )
leapFlag = 1;
else
leapFlag = 0;
I'm writing my own implementation of a Neural Network class in C++. I'm not sure how to refer to the weights this statement:
in = in + (inputs [l] * calcWeights [l]) ;
The reason is because there could be more weights than inputs. Here is my code:
void Train (int numInputs, int numOutputs, double inputs [], double outputs []) {
// Set the Random Seed:
srand (time (0)) ;
// Weights (n input(s) * n output(s) = n weight branch(es)):
double calcWeights [numInputs * numOutputs] ;
// Errors (n input(s) * n output(s) = n error branch(es)):
double errors [numInputs * numOutputs] ;
// Set the Weights to random:
for (int j = 0 ; j < numInputs ; j = j + 1) {
calcWeights [j] = ((-1 * numInputs) + (((double) rand ()) % (1 * numInputs))) ;
}
// Train:
int i = 0 ;
double in = 0 ;
double out [numOutputs] ;
while (i < 14999) {
// Get the estimated output:
for (int k = 0 ; k < numOutputs ; k = k + 1) {
for (int l = 0 ; l < numInputs ; l = l + 1) {
in = in + (inputs [l] * calcWeights [l]) ;
}
out [k] = in + GetBias () ;
}
for (int m = 0 ; m < numOutputs ; m = m + 1) {
error [m] = outputs [m] - out [m]
}
// Increment the iterator:
i = i + 1 ;
}
}
From your clarification in comments, I believe modifying your loop a bit will give you what you want.
for (int k = 0 ; k < numOutputs ; k = k + 1) {
in = 0; //Reset in to 0 at the beginning of each output loop
for (int l = 0 ; l < numInputs ; l = l + 1) {
in = in + (inputs [l] * calcWeights [l + k*numInputs]) ;
}
out [k] = in + GetBias () ;
}
You should also make sure you initialize all the weights above.
for (int j = 0 ; j < (numInputs * numOutputs) ; j = j + 1) {
calcWeights [j] = ((-1 * numInputs) + (((double) rand ()) % (1 * numInputs))) ;
}
For a couple of style choices I just want to point out that you can replace k = k + 1 with simply ++k. Likewise you can replace in = in + ...; with in += ...;
Program: So I made a program that take two numbers, N and L. N is the size of a 2D array and L is a number from 3 - 16. The program builds the array and starts at the center and works its way out in a counter clockwise spiral. I is the value of the center and its as you go through the array( in the spiral ) the value will increase by one. It it is prime, that number will be assigned to that spot and if not it * will take its place instead.
Error: I'm getting a "Floating point exception " error, how would I solve this?
Code:
void Array_Loop( int *Array, int n, int L ) ;
int Is_Prime( int Number ) ;
int main( int argc, char *argv[] ){
int **Array ;
int n, L ;
n = atoi( argv[1] ) ;
L = atoi( argv[2] ) ;
Matrix_Build( &Array, n, n ) ;
Array_Loop( Array, n, L ) ;
return 0 ;
}
void Array_Loop( int *Array, int n, int L ){
int i, j, k, h ;
int lctn, move;
lctn = n / 2 + 1 ;
i = lctn ;
j = lctn ;
move = 1
while( i != 0 && j != n ){
for( j = lctn ; j < lctn + move ; j++ ){
if( L % 2 == 2) Array[i][j] = -1 ;
else Array[i][j] = Is_Prime( L ) ;
L++ ;
}
move = move * -1 ;
for( i = i ; i > lctn - move ; i-- ){
if( L % 2 == 2) Array[i][j] = -1 ;
else Array[i][j] = Is_Prime( L ) ;
L++ ;
}
move-- ;
for( j = j ; j > lctn - move ; j-- ){
if( L % 2 == 2) Array[i][j] = -1 ;
else Array[i][j] = Is_Prime( L ) ;
L++ ;
}
move = move * -1 ;
for( i = i ; i < lctn - move ; i-- ){
if( L % 2 == 2) Array[i][j] = -1 ;
else Array[i][j] = Is_Prime( L ) ;
L++ ;
}
move++ ;
}
}
int Is_Prime( int Number ){
int i ;
for( i = 0 ; i < Number / 2 ; i++ ){
if( Number % i != 0 ) return -1 ;
}
return Number ;
}
You are getting Floating point exception because Number % i, when i is 0:
int Is_Prime( int Number ){
int i ;
for( i = 0 ; i < Number / 2 ; i++ ){
if( Number % i != 0 ) return -1 ;
}
return Number ;
}
Just start the loop at i = 2. Since i = 1 in Number % i it always be equal to zero, since Number is a int.
Floating Point Exception happens because of an unexpected infinity or NaN.
You can track that using gdb, which allows you to see what is going on inside your C program while it runs. For more details:
https://www.cs.swarthmore.edu/~newhall/unixhelp/howto_gdb.php
In a nutshell, these commands might be useful...
gcc -g myprog.c
gdb a.out
gdb core a.out
ddd a.out
I'm working on problem 9 in Project Euler:
There exists exactly one Pythagorean triplet for which a + b + c = 1000.
Find the product abc.
The following code I wrote uses Euclid's formula for generating primes. For some reason my code returns "0" as an answer; even though the variable values are correct for the first few loops. Since the problem is pretty easy, some parts of the code aren't perfectly optimized; I don't think that should matter. The code is as follows:
#include <iostream>
using namespace std;
int main()
{
int placeholder; //for cin at the end so console stays open
int a, b, c, m, n, k;
a = 0; b = 0; c = 0;
m = 0; n = 0; k = 0; //to prevent initialization warnings
int sum = 0;
int product = 0;
/*We will use Euclid's (or Euler's?) formula for generating primitive
*Pythagorean triples (a^2 + b^2 = c^2): For any "m" and "n",
*a = m^2 - n^2 ; b = 2mn ; c = m^2 + n^2 . We will then cycle through
*values of a scalar/constant "k", to make sure we didn't miss anything.
*/
//these following loops will increment m, n, and k,
//and see if a+b+c is 1000. If so, all loops will break.
for (int iii = 1; m < 1000; iii++)
{
m = iii;
for (int ii = 1; n < 1000; ii++)
{
n = ii;
for (int i = 1; k <=1000; i++)
{
sum = 0;
k = i;
a = (m*m - n*n)*k;
b = (2*m*n)*k;
c = (m*m + n*n)*k;
if (sum == 1000) break;
}
if (sum == 1000) break;
}
if (sum == 1000) break;
}
product = a * b * c;
cout << "The product abc of the Pythagorean triplet for which a+b+c = 1000 is:\n";
cout << product << endl;
cin >> placeholder;
return 0;
}
And also, is there a better way to break out of multiple loops without using "break", or is "break" optimal?
Here's the updated code, with only the changes:
for (m = 2; m < 1000; m++)
{
for (int n = 2; n < 1000; n++)
{
for (k = 2; (k < 1000) && (m > n); k++)
{
sum = 0;
a = (m*m - n*n)*k;
b = (2*m*n)*k;
c = (m*m + n*n)*k;
sum = a + b + c;
if ((sum == 1000) && (!(k==0))) break;
}
It still doesn't work though (now gives "1621787660" as an answer). I know, a lot of parentheses.
The new problem is that the solution occurs for k = 1, so starting your k at 2 misses the answer outright.
Instead of looping through different k values, you can just check for when the current sum divides 1000 evenly. Here's what I mean (using the discussed goto statement):
for (n = 2; n < 1000; n++)
{
for (m = n + 1; m < 1000; m++)
{
sum = 0;
a = (m*m - n*n);
b = (2*m*n);
c = (m*m + n*n);
sum = a + b + c;
if(1000 % sum == 0)
{
int k = 1000 / sum;
a *= k;
b *= k;
c *= k;
goto done;
}
}
}
done:
product = a * b * c;
I also switched around the two for loops so that you can just initialize m as being larger than n instead of checking every iteration.
Note that with this new method, the solution doesn't occur for k = 1 (just a difference in how the loops are run, this isn't a problem)
Presumably sum is supposed to be a + b + c. However, nowhere in your code do you actually do this, which is presumably your problem.
To answer the final question: Yes, you can use a goto. Breaking out of multiple nested loops is one of the rare occasions when it isn't considered harmful.
So I had to write a program for a computer project for high school and I thought of doing a sudoko solver. The 'solve' algorithm is implemented like this:-
For any points where only one element 'fits' looking at rows, columns, 3x3 set, put that number in. Do this repeatedly till it can't be done anymore. This is seen in the 'singleLeft' function.
If a number 'fits' in some point but nowhere else in the associated row, column or 3x3 set, put that number in. This can be seen in the 'checkOnlyAllowed' function.
If we're not done yet, do a 'guess' - take some number that 'fits' in the point, put it in there and then solve again using this algorithm (recurse) - if it works, we're done.
So far, I have this code:
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
//Prints a message and exits the application.
void error(const char msg[])
{
cout << "An error occurred!" << endl;
cout << "Description: " << msg << endl;
exit(0);
}
//A representation of a sudoku board. Can be read from a file or from memory.
class Sudoku
{
protected:
//For a point x, y and a number n in the board, mAllowed[x][y][n]
//is 1 if n is allowed in that point, 0 if not.
int mAllowed[9][9][10];
int filledIn;
public:
/*
* For mBoard[i][j], the location is (i,j) in the below map:
*
* (0,0) (0,1) (0,2) (0,3) (0,4) (0,5) (0,6) (0,7) (0,8)
* (1,0) (1,1) (1,2) (1,3) (1,4) (1,5) (1,6) (1,7) (1,8)
* (2,0) (2,1) (2,2) (2,3) (2,4) (2,5) (2,6) (2,7) (2,8)
*
* (3,0) (3,1) (3,2) (3,3) (3,4) (3,5) (3,6) (3,7) (3,8)
* (4,0) (4,1) (4,2) (4,3) (4,4) (4,5) (4,6) (4,7) (4,8)
* (5,0) (5,1) (5,2) (5,3) (5,4) (5,5) (5,6) (5,7) (5,8)
*
* (6,0) (6,1) (6,2) (6,3) (6,4) (6,5) (6,6) (6,7) (6,8)
* (7,0) (7,1) (7,2) (7,3) (7,4) (7,5) (7,6) (7,7) (7,8)
* (8,0) (8,1) (8,2) (8,3) (8,4) (8,5) (8,6) (8,7) (8,8)
*
*/
int mBoard[9][9];
//Read in from file with given name.
Sudoku(char filename[])
{
filledIn = 0;
int i, j, k;
//Fill the board with 0s.
for (i = 0; i < 9; ++i)
for (j = 0; j < 9; ++j)
mBoard[i][j] = 0;
//Set every number to 'allowed' initially.
for (i = 0; i < 9; ++i)
for (j = 0; j < 9; ++j)
for (k = 1; k <= 9; ++k)
mAllowed[i][j][k] = 1;
//Read in from the file.
ifstream file(filename);
if (!file)
error("File doesn't exist!");
for (i = 0; i < 9; ++i)
for (j = 0; j < 9; ++j)
if (file)
{
int m;
file >> m;
if (m)
set(i, j, m);
}
else
error("Not enough entries in file!");
}
//Solve the board!
int solve()
{
int prevFilledIn;
do
{
prevFilledIn = filledIn;
singleLeft();
checkOnlyAllowed();
} while (filledIn - prevFilledIn > 3);
if (filledIn < 81)
guess();
return filledIn == 81;
}
//Given a point i, j, this looks for places where this point
//disallows a number and sets the 'mAllowed' table accordingly.
void fixAllowed(int i, int j)
{
int n = mBoard[i][j], k;
for (k = 0; k < 9; ++k)
mAllowed[i][k][n] = 0;
for (k = 0; k < 9; ++k)
mAllowed[k][j][n] = 0;
//Look in 3x3 sets too. First, set each coordinate to the
//highest multiple of 3 below itself. This takes us to the
//top-left corner of the 3x3 set this point was in. Then,
//add vectorially all points (x,y) where x and y each are
//one of 0, 1 or 2 to visit each point in this set.
int x = (i / 3) * 3;
int y = (j / 3) * 3;
for (k = 0; k < 3; ++k)
for (int l = 0; l < 3; ++l)
mAllowed[x + k][y + l][n] = 0;
mAllowed[i][j][n] = 1;
}
//Sets a point i, j to n.
void set(int i, int j, int n)
{
mBoard[i][j] = n;
fixAllowed(i, j);
++filledIn;
}
//Try using 'single' on a point, ie, only one number can fit in this
//point, so put it in and return 1. If more than one number can fit,
//return 0.
int trySinglePoint(int i, int j)
{
int c = 0, m;
for (m = 1; m <= 9; ++m)
c += mAllowed[i][j][m];
if (c == 1)
{
for (m = 1; m <= 9; ++m)
if (mAllowed[i][j][m])
set(i, j, m);
//printBoard();
return 1;
}
return 0;
}
//Try to solve by checking for spots that have only one number remaining.
void singleLeft()
{
for (;;)
{
for (int i = 0; i < 9; ++i)
for (int j = 0; j < 9; ++j)
if (!mBoard[i][j])
if (trySinglePoint(i, j))
goto logic_worked;
//If we reached here, board is either full or unsolvable by this logic, so
//our job is done.
return;
logic_worked:
continue;
}
}
//Within rows, columns or sets, whether this number is 'allowed' in spots
//other than i, j.
int onlyInRow(int n, int i, int j)
{
for (int k = 0; k < 9; ++k)
if (k != j && mAllowed[i][k][n])
return 0;
return 1;
}
int onlyInColumn(int n, int i, int j)
{
for (int k = 0; k < 9; ++k)
if (k != i && mAllowed[k][j][n])
return 0;
return 1;
}
int onlyInSet(int n, int i, int j)
{
int x = (i / 3) * 3;
int y = (j / 3) * 3;
for (int k = 0; k < 3; ++k)
for (int l = 0; l < 3; ++l)
if (!(x + k == i && y + l == j) && mAllowed[x + k][y + l][n])
return 0;
return 1;
}
//If a number is 'allowed' in only one spot within a row, column or set, it's
//guaranteed to have to be there.
void checkOnlyAllowed()
{
for (int i = 0; i < 9; ++i)
for (int j = 0; j < 9; ++j)
if (!mBoard[i][j])
for (int m = 1; m <= 9; ++m)
if (mAllowed[i][j][m])
if (onlyInRow(m, i, j) || onlyInColumn(m, i, j) || onlyInSet(m, i, j))
set(i, j, m);
}
//Copy from a given board.
void copyBoard(int board[9][9])
{
filledIn = 0;
for (int i = 0; i < 9; ++i)
for (int j = 0; j < 9; ++j)
{
if (board[i][j] > 0)
++filledIn;
mBoard[i][j] = board[i][j];
}
}
//Try to solve by 'guessing'.
void guess()
{
for (int i = 0; i < 9; ++i)
for (int j = 0; j < 9; ++j)
for (int n = 1; n <= 9; ++n)
if (!mBoard[i][j])
if (mAllowed[i][j][n] == 1)
{
//Do a direct copy so that it gets the 'mAllowed'
//table too.
Sudoku s = *this;
//Try solving with this number at this spot.
s.set(i, j, n);
if (s.solve())
{
//It was able to do it! Copy and report success!
copyBoard(s.mBoard);
return;
}
}
}
//Print the board (for debug purposes)
void printBoard()
{
for (int i = 0; i < 9; ++i)
{
for (int j = 0; j < 9; ++j)
cout << mBoard[i][j] << " ";
cout << endl;
}
cout << endl;
char s[5];
cin >> s;
}
};
int main(int argc, char **argv)
{
//char filename[42];
//cout << "Enter filename: ";
//cin >> filename;
char *filename = argv[1];
Sudoku s(filename);
if (!s.solve())
error("Couldn't solve!");
cout << "Solved! Here's the solution:" << endl << endl;
for (int i = 0; i < 9; ++i)
{
for (int j = 0; j < 9; ++j)
cout << s.mBoard[i][j] << " ";
cout << endl;
}
return 0;
}
(code including line numbers: http://sprunge.us/AiUc?cpp)
Now I understand that it isn't very good style, but it came out of a late-night coding session and also we use an older compiler in the school lab so I had to do some things differently (in that compiler, the standard headers have the '.h' extension, variables declared in for loops are in outside-for scope, ... ).
The file should contain whitespace-delimited digits for each spot in the board starting from the top-left going left to right and top to bottom, with empty spots signified by '0's.
For the following file, it works rather well:
5 3 0 0 7 0 0 0 0
6 0 0 1 9 5 0 0 0
0 9 8 0 0 0 0 6 0
8 0 0 0 6 0 0 0 3
4 0 0 8 0 3 0 0 1
7 0 0 0 2 0 0 0 6
0 6 0 0 0 0 2 8 0
0 0 0 4 1 9 0 0 5
0 0 0 0 8 0 0 7 9
However, this one gives it trouble:
0 9 4 0 0 0 1 3 0
0 0 0 0 0 0 0 0 0
0 0 0 0 7 6 0 0 2
0 8 0 0 1 0 0 0 0
0 3 2 0 0 0 0 0 0
0 0 0 2 0 0 0 6 0
0 0 0 0 5 0 4 0 0
0 0 0 0 0 8 0 0 7
0 0 6 3 0 4 0 0 8
If I comment out the print statements and track the progress I can see that it starts by heading out in the wrong direction at points. Eventually it gets stuck toward the end and the backtracking never gets far back enough. I think it's something wrong with the 'checkOnlyAllowed' part...
What do you think could be the problem?
Also - I know I could've used a bitfield for the 'mAllowed' table but we don't officially know about bitwise operations yet in school. :P
At line 170 you have a goto that is jumping out of a for loop, then continuing. This could give you some weird behavior with continuing the wrong loop, behavior that might depend on the specific compiler.
Try replacing lines 164-177 with:
164 for (;;)
165 {
166 bool successfullyContributedToTheBoard = false;
167 for (int i = 0; i < 9; ++i)
168 for (int j = 0; j < 9; ++j)
169 if (!mBoard[i][j])
170 if (trySinglePoint(i, j))
171 successfullyContributedToTheBoard = true;
172 if (!successfullyContributedToTheBoard)
173 return;
174 }
I didn't look at your code but your strategy is exactly the same as the one I used to code a Sudoku solver. But I can't remember it being very slow. I got solutions in an instant. The maximum number of "guesses" the program had do make was 3 during my tests. That was for Sudoku problems which were supposed to be very hard. Three is not a big number with respect to back tracking and you can pick a cell which has only a few possibilities left (two or three) which limits the search space to about 20-30 states only (for hard Sudoku problems).
What I'm saying is, it's possible to use this strategy and solve Sudoku problems really fast. You only have to figure out how to optimize your code. Try to avoid redundant work. Try to remember things so you don't need to recalculate them again and again.
Alright, I got it working! It seems that the i, j loop within 'guess' was unecessary - ie., it should only do a guess on one empty spot because its 'child processes' will handle the rest. Fixing this actually made the code simpler. Now it works really well, and actually its very quick!
Thanks for your help, everyone. ;-)