leetcode：sudoku solver

标签：leetcode   java   遍历   回溯   数独   

sudoku solver，题意如下：

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.

既然有多种解，那就只能一个个可能的试过去，试到一种解就可以输出了。

具体的用可以理解的话来说，过程是这样的：

遍历整个数独表格，一旦碰到一个空位，就往里填个1，然后判断这个1是否在所在的行和列和小的九宫格里是可行的，如果可行，就往下遍历，如果不可行，就填2，重复上面的操作，一直试到9为止。

先贴上代码：

public static void solveSudoku(char[][] board) {
		sudoku(board);
    }
	
	 static boolean sudoku(char[][] board){
		for(int i=0;i<9;i++){
			for(int j=0;j<9;j++){
				if(board[i][j] == '.'){
					for(int k=1;k<=9;k++){
						board[i][j] = (char)('0'+k);
						if(isValid(board, i, j) && sudoku(board)){
							return true;
						}
						board[i][j] = '.';
					}
					return false;
				}
			}
		}
		return true;
	}
	
	 static boolean isValid(char[][] board,int i,int j){
		for(int a=0;a<9;a++){
			if(board[i][j] == board[i][a] && a!=j)return false;
			if(board[i][j] == board[a][j] && a!=i)return false;
		}
		for(int a=3*(i/3);a<3*(i/3+1);a++){
			for(int b=3*(j/3);b<3*(j/3+1);b++){
				if(a!=i && b!=j && board[a][b] == board[i][j]){
					return false;
				}
			}
		}
		return true;
	}
	
	public static void main(String[] args) {
		char[][] a = {{'.','.','9','7','4','8','.','.','.'},
				      {'7','.','.','.','.','.','.','.','.'},
				      {'.','2','.','1','.','9','.','.','.'},
				      {'.','.','7','.','.','.','2','4','.'},
				      {'.','6','4','.','1','.','5','9','.'},
				      {'.','9','8','.','.','.','3','.','.'},
				      {'.','.','.','8','.','3','.','2','.'},
				      {'.','.','.','.','.','.','.','.','6'},
				      {'.','.','.','2','7','5','9','.','.'}};
		solveSudoku(a);
		for(int i=0;i<9;i++){
			for(int j=0;j<9;j++){
				System.out.print(a[i][j]+" ");
			}
			System.out.println();
		}
	}

leetcode：sudoku solver

标签：leetcode   java   遍历   回溯   数独   

原文地址：http://blog.csdn.net/gotobar/article/details/45059391