Leetcode dfs Binary Tree Postorder Traversal II

Sudoku Solver

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Submissions: 56537My Submissions

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.

题意：填充数独，返回是否填充成功

思路：dfs

找一个还没填充的位置，尝试填写0-9其中的一个数字，判断是否理。

如果合理，则可以转移到一个同样子问题，所以可以采用递归的方式实现。

bool solveSudoku(vector<vector<char> >&board)

返回是否成功填充当前状态为 board的数独

bool isValid(const vector<vector<char> >&board, int x, int y){
	//检查行
	for(int j = 0; j < 9; ++j) if(j != y && board[x][j] == board[x][y]) return false;
	//检查列
	for(int i = 0; i < 9; ++i) if(i != x && board[i][y] == board[x][y]) return false;
	//检查小方块
	for(int i = 0; i < 3; ++i)
		for(int j = 0; j < 3; ++j){
			if(!(x/3 * 3 + i == x && y /3 * 3 + j == y) && board[x/3 * 3 + i][y /3 * 3 + j] == board[x][y]) return false;
		}
	return true;
}

bool solveSudoku(vector<vector<char> >&board)
{
	for(int i = 0; i < 9;  ++i){
		for(int j = 0; j < 9; ++j){
			if(board[i][j] == '.'){
				for(int k = 0; k < 9; ++k){
					board[i][j] = k + '1' ;
					if(isValid(board, i, j) && solveSudoku(board)) return true;
					board[i][j] = '.';
				}
				return false;
			}
		}
	}
	return true; //漏写了这句，WA了好多次
}