LeetCode进阶之路（ Sudoku Solver）

Write a program to solve a Sudoku puzzle by filling the empty cells.

Empty cells are indicated by the character '.'.

You may assume that there will be only one unique solution.

A sudoku puzzle...

...and its solution numbers marked in red.

题目：把数独给解出来。。

思路：采用回溯法，一点点尝试着填数，不行的话就回溯，直到都填满就返回。

 

public void solveSudoku(char[][] board) {
        healper(board);
	}
	
	public boolean healper(char[][] board) {
		for (int i = 0; i < board.length; i++) {
			for (int j = 0; j < board[0].length; j++) {
				if (board[i][j] == '.') {
					for (char z = '1'; z <= '9'; z++) {
						if (isValid(board, i, j, z)) {
							board[i][j] = z;
							if (healper(board))
								return true;//有解
							else
								board[i][j] = '.';// 回退
						}
					}
					return false;
				}

			}
		}
		return true;
	}
	
	private boolean isValid(char[][] board, int i, int j, char c) {
		// 检查行
		for (int row = 0; row < 9; row++)
			if (board[row][j] == c)
				return false;

		// 检查列
		for (int col = 0; col < 9; col++)
			if (board[i][col] == c)
				return false;

		// 检查9宫格
		for (int row = i / 3 * 3; row < i / 3 * 3 + 3; row++)
			for (int col = j / 3 * 3; col < j / 3 * 3 + 3; col++)
				if (board[row][col] == c)
					return false;

		return true;
	}

种一棵树最好的时间是十年前，其次是现在！