【leetcode】37.（Hard）Sudoku

题目链接

DFS+回溯法

提交代码：

class Solution {
	public void solveSudoku(char[][] board) {
		if (board == null || board.length == 0)
			return;

		fillBoard(board);
	}

	public boolean fillBoard(char[][] board) {
		for (int i = 0; i < 9; i++) {
			for (int j = 0; j < 9; j++) {
				if (board[i][j] == '.') {
					for (char num = '1'; num <= '9'; num++) {
						if (isValid(board, i, j, num)) {
							board[i][j] = num;
						if (fillBoard(board))
							return true;
						else
							board[i][j] = '.';
					}
					}
					return false;
				}
				
			}
		}
		return true;
	}

	public boolean isValid(char[][] board, int row, int column, char num) {
		int i, j;
		// check row
		for (j = 0; j < 9; j++)
			if (j != column && board[row][j] == num)
				return false;

		// check column
		for (i = 0; i < 9; i++)
			if (i != row && board[i][column] == num)
				return false;

		// check sub block
		for (i = row / 3 * 3; i < row / 3 * 3 + 3; i++)
			for (j = column / 3 * 3; j < column / 3 * 3 + 3; j++)
				if ((i != row || j != column) && board[i][j] == num)
					return false;

		return true;
	}

}

运行结果：