LeetCode-37.Sudok Solver

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

A sudoku solution must satisfy all of the following rules:

1. Each of the digits 1-9 must occur exactly once in each row.
2. Each of the digits 1-9 must occur exactly once in each column.
3. Each of the the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.

Empty cells are indicated by the character '.'.

A sudoku puzzle...

...and its solution numbers marked in red.

Note:

• The given board contain only digits 1-9 and the character '.'.
• You may assume that the given Sudoku puzzle will have a single unique solution.
• The given board size is always 9x9.

判断当前插入的值有没有错误，没有继续填下面的

class Solution {//剪枝 mytip
    public void solveSudoku(char[][] board) {
        if(null==board ||0==board.length)
            return;
        help(board);
    }
    private boolean help(char[][] board){
        for (int row = 0; row < board.length; row++) {
            for (int col = 0; col < board.length; col++) {
                if('.'==board[row][col]){
                    for (char i = '1'; i <= '9'; i++) {
                        if(isValidSudoku(board,row,col,i)){
                            board[row][col]=i;
                            if(help(board)){
                                return true;
                            }
                            else{
                                board[row][col]='.';
                            }
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
    private boolean isValidSudoku(char[][] board,int row,int col,char ch) {
        for (int i = 0; i <board.length ; i++) {
            if(ch==board[row][i]||ch==board[i][col]){
                return false;
            }
        }
        int r = row/3*3;
        int c = col/3*3;
        for (int i = r; i <r+3 ; i++) {
            for (int j = c; j < c+3 ; j++) {
                if(ch==board[i][j]){
                    return false;
                }
            }
        }

        return true;
    }
}

 另外可以通过以下方式加速

• 从选项少的格子开始
• 先使用n*n的循环，查找所有空格的可选数，根据可选数排序，从可选数少的开始填写
• 用Dancing Links http://www.cnblogs.com/grenet/p/3145800.html    https://www.cnblogs.com/grenet/p/3163550.html

相关题

有效的数独 LeetCode36 https://www.cnblogs.com/zhacai/p/10622779.html