leetcode 37. Sudoku Solver

public class Solution {

public static void main(String[] args) {
char[][] input = {
{'5','3','.','.','7','.','.','.','.'},
{'6','.','.','1','9','5','.','.','.'},
{'9','8','.','.','.','.','.','6','.'},
{'8','.','.','.','6','.','.','.','3'},
{'4','.','.','8','.','3','.','.','1'},
{'7','.','.','.','2','.','.','.','6'},
{'.','6','.','.','.','.','2','8','.'},
{'.','.','.','4','1','9','.','.','5'},
{'.','.','.','.','8','.','.','7','9'}
};
solveSudoku(input);
}

public static void solveSudoku(char[][] board) {
solve(board);
for(int i = 0;i<9;i++){
for(int j = 0;j<9;j++){
System.out.print(board[i][j]);
}
System.out.println();
}
}

public static boolean solve(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++){						//给'.'的位置按顺序赋1-9的值
board[i][j] = m;
if(isValid(board,i,j)&&solve(board)){			//检查赋值后的矩阵是否合法，并迭代检查到最后是否合法
return true;
}
board[i][j] = '.';
}
return false;
}
}
}
return true;
}

public static boolean isValid(char[][] board, int row ,int col){	//看是否在同行同列同九个格中有相同的值
for(int i = 0;i<9;i++){
if(i != row && board[i][col] == board[row][col]){
return false;
}
}
for(int i = 0;i<9;i++){
if(i!=col && board[row][i] == board[row][col]){
return false;
}
}
int beginRow = 3*(row/3);
int beginCol = 3*(col/3);
for(int i = beginRow;i<beginRow+3;i++){
for(int j = beginCol;j<beginCol+3;j++){
if(i!=row&&j!=col&&board[i][j] == board[row][col]){
return false;
}
}
}
return true;
}

}