leetcode 37. 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.

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判断是不是数独，这题还是有点难度的，想到的办法就是对没有填入数字的位置进行测试，目前合理则前进，不合理则回退，1-9都不行就返回FALSE
public class Solution {
public void solveSudoku(char[][] board) {
helper(board);
}
public boolean helper(char[][]board){
for(int i=0;i<9;i++){
for(int j=0;j<9;j++){
if(board[i][j]=='.'){
for(char m='1';m<='9';m++){
if(isvalid(board,i,j,m)){
board[i][j]=m;
if(!helper(board))board[i][j]='.';
else return true;
}
}
return false;
}
}
}
return true;
}
public boolean isvalid(char[][]board,int i,int j,char c){
//row
for(int m=0;m<9;m++){
if(board[i][m]==c)return false;
}
//column
for(int n=0;n<9;n++){
if(board
[j]==c)return false;
}
//inner
for(int m=i/3*3;m<i/3*3+3;m++){
for(int n=j/3*3;n<j/3*3+3;n++){
if(board[m]
==c)return false;
}
}
return true;
}
}