Backtracking crossword algorithm in c - c

Question

So i made a backtracking algorithm in c, where i get a txt file filled with words in each line and another txt file just has coordinates for the black squares of a square crossword. I know my implementation is extremelly simple, but i just want to have the barebones algorithm, to make it much faster later on with constraint satisfaction, forward checking etc.
However i have no idea how to get the basic code to work without segmentation faults and wrong solutions! Ant advice would be very helpful!
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX_WORDS 150000
#define MAX_DIMENSION 200
#define MAX_BLACK_SQUARES 250
int is_valid_word(char *word, int dimension, char crossword[MAX_DIMENSION][MAX_DIMENSION])
{
int i, j, k;
int word_length = strlen(word);
// check if word is too long
if (word_length > dimension)
{
return 0;
}
// check if word overlaps existing letters
for (i = 0; i < dimension; i++)
{
for (j = 0; j < dimension; j++)
{
if (crossword[i][j] != '_')
{
for (k = 0; k < word_length; k++)
{
if ((i + k < dimension && crossword[i + k][j] != '_' && crossword[i + k][j] != word[k]) ||
(j + k < dimension && crossword[i][j + k] != '_' && crossword[i][j + k] != word[k]))
{
return 0;
}
}
}
}
}
return 1;
}
int solve_crossword(int dimension, char crossword[MAX_DIMENSION][MAX_DIMENSION], char words[MAX_WORDS][30], int num_words, int word_index)
{
int i, j, k;
if (word_index >= num_words)
{
// all words have been placed, so return true
return 1;
}
// try placing the current word horizontally
for (i = 0; i < dimension; i++)
{
for (j = 0; j < dimension - strlen(words[word_index]); j++)
{
if (crossword[i][j] != '#')
{
// try placing the word here
int is_valid = 1;
for (k = 0; k < strlen(words[word_index]); k++)
{
if (crossword[i][j + k] != '_' && crossword[i][j + k] != words[word_index][k])
{
is_valid = 0;
break;
}
}
if (is_valid)
{
// place the word
for (k = 0; k < strlen(words[word_index]); k++)
{
crossword[i][j + k] = words[word_index][k];
}
// recursive call to place the next word
if (solve_crossword(dimension, crossword, words, num_words, word_index + 1))
{
return 1;
}
// backtrack by removing the word
for (k = 0; k < strlen(words[word_index]); k++)
{
crossword[i][j + k] = '_';
}
}
}
}
}
// try placing the current word vertically
for (i = 0; i < dimension - strlen(words[word_index]); i++)
{
for (j = 0; j < dimension; j++)
{
if (crossword[i][j] != '#')
{
// try placing the word here
int is_valid = 1;
for (k = 0; k < strlen(words[word_index]); k++)
{
if (crossword[i + k][j] != '_' && crossword[i + k][j] != words[word_index][k])
{
is_valid = 0;
break;
}
}
if (is_valid)
{
// place the word
for (k = 0; k < strlen(words[word_index]); k++)
{
crossword[i + k][j] = words[word_index][k];
}
// recursive call to place the next word
if (solve_crossword(dimension, crossword, words, num_words,word_index + 1))
{
return 1;
}
// backtrack by removing the word
for (k = 0; k < strlen(words[word_index]); k++)
{
crossword[i + k][j] = '_';
}
}
}
}
}
// if we get here, we were unable to place the word in either direction
return 0;
}
int main()
{
// open dictionary file
FILE *dict_file = fopen("dicts/EvenMoreWords.txt", "r");
if (dict_file == NULL)
{
printf("Unable to open dict.txt\n");
return 1;
}
// read dictionary into array
char words[MAX_WORDS][30];
int num_words = 0;
char buffer[30];
while (fgets(buffer, 30, dict_file) != NULL)
{
int word_length = strlen(buffer);
if (buffer[word_length - 1] == '\n')
{
buffer[word_length - 1] = '\0';
}
strcpy(words[num_words], buffer);
num_words++;
}
fclose(dict_file);
// open crossword file
FILE *crossword_file = fopen("crosswords/c1.txt", "r");
if (crossword_file == NULL)
{
printf("Unable to open crossword.txt\n");
return 1;
}
// read dimensions and black squares
int dimension, i, j, width, height;
fscanf(crossword_file, "%d", &dimension);
// initialize crossword
char crossword[MAX_DIMENSION][MAX_DIMENSION];
while (fscanf(crossword_file, "%d %d", &width, &height) != EOF)
{
crossword[width - 1][height - 1] = '#';
}
printf("\n\n\n");
for (i = 0; i < dimension; i++)
{
for (j = 0; j < dimension; j++)
{
if (crossword[i][j] != '#')
{
crossword[i][j] = '_';
printf("%c ", crossword[i][j]);
}
else
{
printf("%c ", crossword[i][j]);
}
}
printf("\n");
}
printf("\n\n\n");
// solve crossword
if (solve_crossword(dimension, crossword, words, num_words, 0))
{
// print solution
for (i = 0; i < dimension; i++)
{
for (j = 0; j < dimension; j++)
{
printf("%c ", crossword[i][j]);
}
printf("\n");
}
}
else
{
printf("Unable to find a solution\n");
}
return 0;
}