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// 37. Sudoku Solver
#include "leetcode.h"
/*
* write a program to solve a sudoku puzzle by filling the empty cells. a sudoku
* solution must satisfy all of the following rules. each of the digits '1-9'
* must occur exactly once in each row, each of the digits '1-9', must occur
* exactly once in each column, and each of the digits '1-9' must occur exactly
* once in each of the 9 3x3 sub-boxes of the grid. the '.' character indicates
* empty cells.
*/
bool solve(char **board, bool row[9][9], bool col[9][9], bool grid[9][9], int r,
int c) {
if (r == 9)
return true;
int next_r = c == 8 ? r + 1 : r;
int next_c = c == 8 ? 0 : c + 1;
if (board[r][c] != '.')
return solve(board, row, col, grid, next_r, next_c);
int grid_idx = (r / 3) * 3 + (c / 3);
for (int i = 0; i < 9; i++) {
if (!row[r][i] && !col[c][i] && !grid[grid_idx][i]) {
board[r][c] = '1' + i;
row[r][i] = col[c][i] = grid[grid_idx][i] = true;
if (solve(board, row, col, grid, next_r, next_c))
return true;
board[r][c] = '.';
row[r][i] = col[c][i] = grid[grid_idx][i] = false;
}
}
return false;
}
void solveSudoku(char **board, int boardSize, int *boardColSize) {
if (boardSize != 9 || *boardColSize != 9)
return;
bool row[9][9] = {false};
bool col[9][9] = {false};
bool grid[9][9] = {false};
for (int i = 0; i < 9; i++)
for (int j = 0; j < 9; j++)
if (board[i][j] != '.') {
int num = board[i][j] - '1';
if (num < 0 || num >= 9)
return;
row[i][num] = col[j][num] = true;
grid[(i / 3) * 3 + (j / 3)][num] = true;
}
solve(board, row, col, grid, 0, 0);
}
int main() {
char *board[] = {{"5", "3", ".", ".", "7", ".", ".", ".", "."},
{"6", ".", ".", "1", "9", "5", ".", ".", "."},
{".", "9", "8", ".", ".", ".", ".", "6", "."},
{"8", ".", ".", ".", "6", ".", ".", ".", "3"},
{"4", ".", ".", "8", ".", "3", ".", ".", "1"},
{"7", ".", ".", ".", "2", ".", ".", ".", "6"},
{".", "6", ".", ".", ".", ".", "2", "8", "."},
{".", ".", ".", "4", "1", "9", ".", ".", "5"},
{".", ".", ".", ".", "8", ".", ".", "7", "9"}};
solveSudoku((char **)board, ARRAY_SIZE(board), ARRAY_SIZE(board[0]));
for (int i = 0; i < ARRAY_SIZE(board); i++) {
for (int j = 0; j < ARRAY_SIZE(board[0]); j++)
printf("%c ", board[i][j]);
printf("\n");
}
}
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