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public class SudokuSolver {
public void solveSudoku(char[][] board) {
if (board == null || board.length != 9) {
return;
}
helper(board);
}
private boolean helper(char[][] board) {
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
if (board[i][j] == '.') {
for (char v = '1'; v <= '9'; v++) {
if (isValid(board, i, j, v)) {
board[i][j] = v;
if (helper(board)) {
return true;
} else {
board[i][j] = '.';
}
}
}
return false;
}
}
}
return true;
}
private boolean isValid(char[][] board, int x, int y, char c) {
for (int i = 0; i < 9; i++) {
if (board[x][i] == c || board[i][y] == c) {
return false;
}
}
int xStart = x / 3 * 3;
int yStart = y / 3 * 3;
for (int i = xStart; i < xStart + 3; i++) {
for (int j = yStart; j < yStart + 3; j++) {
if (board[i][j] == c) {
return false;
}
}
}
return true;
}
}
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