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| class Solution {
public void solveSudoku(char[][] board) {
solveSudoku(board, 0);
}
private boolean solveSudoku(char[][] board, int index) {
int m = board.length, n = board[0].length;
if (index == m * n) {
return true;
}
int i = index / n, j = index % m;
if (board[i][j] == '.') {
for (char k = '1'; k <= '9'; k++) {
if (canFill(board, i, j, k)) {
board[i][j] = k;
if (solveSudoku(board, index + 1)) {
return true;
}
board[i][j] = '.';
}
}
} else {
return solveSudoku(board, index + 1);
}
return false;
}
private boolean canFill(char[][] board, int i, int j, char c) {
int m = board.length, n = board[0].length;
for (int rowIndex = 0; rowIndex < i; rowIndex++) {
if (board[rowIndex][j] == c) {
return false;
}
}
for (int rowIndex = i + 1; rowIndex < m; rowIndex++) {
if (board[rowIndex][j] == c) {
return false;
}
}
for (int colIndex = 0; colIndex < j; colIndex++) {
if (board[i][colIndex] == c) {
return false;
}
}
for (int colIndex = j; colIndex < n; colIndex++) {
if (board[i][colIndex] == c) {
return false;
}
}
int rowIndex = i / 3 * 3, colIndex = j / 3 * 3;
for (int k = rowIndex; k < rowIndex + 3; k++) {
for (int l = colIndex; l < colIndex + 3; l++) {
if (k == i && l == j) {
continue;
} else {
if (board[k][l] == c) {
return false;
}
}
}
}
return true;
}
}
|