Word search algorithm segmentation fault - c++

Question

i've been working on word search algorithm for quite long I think i made it good and decided to test limits. I've created program which makes file as big as I want to. So i made a matrix 10000 * 10000 (10000000 letters) and really long word from top left corner to bottom right corner. Thing is that it works with 4000 * 4000 matrix but then it gets bigger it just crashes. I tried to comment all other checkings for possible location and left the right one and it works perfectly even with 10000 * 10000 matrix but as soon as I add other checks it stops and I have no idea why. Any suggestions?
My code:
#include <iostream> //Might Be:
#include <string> // <----->
#include <fstream> // /-\ (1)/\ /\(3)
#include <new> // | \ /
#include <cstdlib> // | \ /
// | \ /
// | \ /
// | \ /
// \_/ (2)\/ \/(4)
//
using namespace std;
//Loop[4] //Loop[5]
int * Possibles(int Widht, int Height, int Poz, int Poz1, int Leng, int * Possible)
{
if(Poz1 < Widht - Leng + 1) // To right
{
Possible[0] = 1;
}
if(Poz1 >= Leng - 1) // To left
{
Possible[1] = 1;
}
if(Poz <= Height - Leng) // From top to bottom
{
Possible[2] = 1;
}
if(Poz >= Leng) // From bottom to top
{
Possible[3] = 1;
}
if(Poz + Leng <= Height && Poz1 + Leng <= Widht) //(2)
{
Possible[4] = 1;
}
if(Poz + Leng <= Height && Poz1 - Leng + 1 >= 0) //(4)
{
Possible[5] = 1;
}
if(Poz - Leng + 1 >= 0 && Poz1 - Leng + 1 >= 0) //(1)
{
Possible[6] = 1;
}
if(Poz - Leng + 1 >= 0 && Poz1 + Leng <= Widht) //(3)
{
Possible[7] = 1;
}
return Possible;
}
int * Zero(int * Possible)
{
Possible[0] = 0;
Possible[1] = 0;
Possible[2] = 0;
Possible[3] = 0;
Possible[4] = 0;
Possible[5] = 0;
Possible[6] = 0;
Possible[7] = 0;
return Possible;
}
string Next(string * NewMatrix, int Height, int Widht)
{
return NewMatrix[Height].substr(Widht, 1);
}
bool Find(string Word, int Poz, int Poz1, int Look, string Have, string * Matrix, int * Possible, int Backup, int Backup1)
{
if(Have == Word)
{
return true;
return Possible;
}
string NewLet = Word.substr(Look, 1);
if(Possible[0] == 1)
{
if(NewLet == Next(Matrix, Poz, Poz1 + 1))
{
Have += NewLet;
return Find(Word, Poz, Poz1 + 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[0] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[1] == 1)
{
if(NewLet == Next(Matrix, Poz, Poz1 - 1))
{
Have += NewLet;
return Find(Word, Poz, Poz1 - 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[1] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[2] == 1)
{
if(NewLet == Next(Matrix, Poz + 1, Poz1))
{
Have += NewLet;
return Find(Word, Poz + 1, Poz1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[2] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[3] == 1)
{
if(NewLet == Next(Matrix, Poz - 1, Poz1))
{
Have += NewLet;
return Find(Word, Poz - 1, Poz1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[3] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[4] == 1)
{
if(NewLet == Next(Matrix, Poz + 1, Poz1 + 1))
{
Have += NewLet;
return Find(Word, Poz + 1, Poz1 + 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[4] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[5] == 1)
{
if(NewLet == Next(Matrix, Poz + 1, Poz1 - 1))
{
Have += NewLet;
return Find(Word, Poz + 1, Poz1 - 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[5] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[6] == 1)
{
if(NewLet == Next(Matrix, Poz - 1, Poz1 - 1))
{
Have += NewLet;
return Find(Word, Poz - 1, Poz1 - 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[6] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
if(Possible[7] == 1)
{
if(NewLet == Next(Matrix, Poz - 1, Poz1 + 1))
{
Have += NewLet;
return Find(Word, Poz - 1, Poz1 + 1, Look + 1, Have, Matrix, Possible, Backup, Backup1);
}
else
{
Possible[7] = 0;
Have = Word.substr(0, 1);
return Find(Word, Backup, Backup1, 1, Have, Matrix, Possible, Backup, Backup1);
}
}
return false;
}
string Diro(int * Possible)
{
string Dir;
bool Next = true;
if(Possible[0] == 1 && Next == true)
{
Dir = " From right to left";
Next = false;
}
if(Possible[1] == 1 && Next == true)
{
Dir = " From left to right";
Next = false;
}
if(Possible[2] == 1 && Next == true)
{
Dir = " From top to bottom";
Next = false;
}
if(Possible[3] == 1 && Next == true)
{
Dir = " From bottom to top";
Next = false;
}
if(Possible[4] == 1 && Next == true)
{
Dir = " ";
Next = false;
}
if(Possible[5] == 1 && Next == true)
{
Dir = " ";
Next = false;
}
if(Possible[6] == 1 && Next == true)
{
Dir = " ";
Next = false;
}
if(Possible[7] == 1 && Next == true)
{
Dir = " ";
Next = false;
}
return Dir;
}
int main()
{
int Height = 0, Widht = 0, Numb = 0;
int Loop[] = {0, 0, 0, 0, 0, 0, 0, 0, 0};
int * Possible = new int[8];
string Dir, Search, Tempo, Temp;
ifstream Data("C:/Users/Magician/AppData/Local/VirtualStore/Program Files (x86)/CodeBlocks/MakeMaze/Files/Maze.txt");
Data >> Widht >> Height;
string * NewMatrix = new string[Height];
while(Loop[7] < Height)
{
Tempo = "";
Loop[8] = 0;
while(Loop[8] < Widht)
{
Data >> Temp;
Tempo += Temp;
Loop[8]++;
}
NewMatrix[Loop[7]] = Tempo;
Loop[7]++;
}
Data >> Numb;
string * Words = new string[Numb];
while(Loop[2] < Numb)
{
Data >> Words[Loop[2]];
Loop[2]++;
}
Data.close();
while(Loop[3] < Numb)
{
Search = Words[Loop[3]].substr(0, 1);
Loop[4] = 0;
while(Loop[4] < Height)
{
Loop[5] = 0;
while(Loop[5] < Widht)
{
if(NewMatrix[Loop[4]].substr(Loop[5], 1) == Search)
{
Zero(Possible);
Possibles(Widht, Height, Loop[4], Loop[5], Words[Loop[3]].size(), Possible);
if(Find(Words[Loop[3]], Loop[4], Loop[5], 1, Search, NewMatrix, Possible, Loop[4], Loop[5]))
{
cout << Words[Loop[3]] << " At: " << Loop[4] + 1 << " collumn, symbol " << Loop[5] + 1 << " " << Diro(Possible) << endl;
Loop[5] = Widht;
Loop[4] = Height;
}
}
Loop[5]++;
}
Loop[4]++;
}
Loop[3]++;
}
delete [] Possible;
delete [] Words;
delete [] NewMatrix;
return 0;
}
If you didn't understood what I wrote before: when I comment every if(Possible[] == )
except for if(Possible[5] == 1) in function Find() algorithm works then all allowed it doesn't. I've tried with 100 * 100 matrix with a lot of words to find and everything's ok.

Answer 1

One condition in Possibles is incorrect:
/* INCORRECT: Should be [ Poz >= Leng - 1 ] */
if(Poz >= Leng) // From bottom to top
{
Possible[3] = 1;
}
But this one is only a logical error and should not cause segmentation faults.
It looks like you have encountered a stack overflow.
Let's do simple calculation. For 10000 * 10000 matrix and word length of 10000, if you start calling Find() at the top left of the matrix, then three directions are possible. In worst case, Find() will traverse about 10000*3 elements. Note in Func() there are 3 string instances (sizeof(string) == 24 in 32bit VC2013), plus various integers. The size of a single frame could easily exceed 100 bytes. Since you are using recursive calls, this could lead to a stack usage of at least 10000 * 3 * 100 = 3000000bytes = approx. 3M.
This number is not very large, but enough for a stack overflow since Windows has a default stack size of 1M. (http://msdn.microsoft.com/en-us/library/8cxs58a6.aspx)
Advice for improvements
This is my used pattern to solve this kinds of matrix traversal problems.
First, define an constant array to hold offsets for movements (Moore neighborhood):
const int delta[8][2] = {
{ 1, 0 }, { 1, 1 }, { 0, 1 }, { -1, 1 },
{ -1, 0 }, { -1, -1 }, { 0, -1 }, { 1, -1 }
};
Second, use a single for to check for all directions:
int initial_x = .., initial_y = ..;
for (int dir = 0; dir < 8; dir++) {
for (int count = 0; count < WORD_LENGTH; count++) {
int current_x = initial_x + delta[dir][0] * count;
int current_y = initial_y + delta[dir][1] * count;
if (IS_INVALID(current_x, current_y)) {
break;
}
}
}
Last, insert various code and flags to complete the program.
Another hint: you can use char type to get and compare a single character in a string (Use word[idx] to get idxth character of word). This could be substantially faster than using substr.