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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");
+ }
+}