[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.
solve里，第一个return true代表能够完成填表，第二个return false代表这个格子试过了1 - 9所有数字都没有return true过，代表都不行，所以return false；第三个return true所有格子都遍历完了，说明填完了，所以return true。

public class Solution {
public void solveSudoku(char[][] board) {
solve(board);
}
private boolean solve(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)(k + '0');
if(isValid(board, i, j) && solve(board)){
return true;
}
board[i][j] = '.';
}
return false;
}
}
}
return true;
}
private boolean isValid(char[][] board, int i, int j){
for(int k = 0; k < 9; k++){
if(k != j && board[i][k] == board[i][j]) return false;
}
for(int k = 0; k < 9; k++){
if(k != i && board[k][j] == board[i][j]) return false;
}
for(int row = i / 3 * 3; row < i / 3 * 3 + 3; row++){
for(int col= j / 3 * 3; col < j / 3 * 3 + 3; col++){
if((row != i || col != j) && board[row][col]==board[i][j]) return false;
}
}
return true;
}
}