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