Leetcode Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

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解题思路：

首先检查是否是9*9 矩阵；

其次依次检查每行，每列和内部各个3*3 矩阵是否满足要求。

建立int[] temp, temp.length = 9 来存储1-9 的个数，当temp[i] > 1时，说明有重复数字出现，返回false.

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Java code:

public class Solution {
    public boolean isValidSudoku(char[][] board) {
       if(board == null || board.length !=9 || board[0].length != 9){
           return false;
       }
       //check each row
       for(int i = 0; i < 9; i++){
           int[] temp = new int[9];
           for(int j = 0; j < 9; j++){
               if(board[i][j] != '.'){
                   temp[board[i][j] - '1']++;
                   if(temp[board[i][j] - '1'] > 1){
                       return false;
                   }
               }
           }
       }
       //check each column
       for(int j = 0; j < 9; j++){
           int[] temp = new int[9];
           for(int i = 0; i < 9; i++){
               if(board[i][j] != '.'){
                   temp[board[i][j] - '1']++;
                   if(temp[board[i][j] - '1'] > 1){
                       return false;
                   }
               }
           }
       }
       //check each 3*3 matrix
       for(int i = 0; i < 3; i++) {
           for(int j = 0; j < 3; j++){
               int[] temp = new int[9];
               for(int m = 3*i; m < 3+3*i; m++){
                   for(int n = 3*j; n < 3+3*j; n++) {
                       if(board[m][n] != '.'){
                           temp[board[m][n] - '1']++;
                           if(temp[board[m][n] - '1'] > 1){
                               return false;
                           }
                       }
                   }
               }
           }
       }
       return true;
    }
}

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Reference:

1. https://leetcode.com/discuss/52006/simple-java-solution-using-three-iterations-all-three-cases