LeetCode -- Valid Sudoku

题目描述：


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 '.'.


验证一个数独的合法性。


思路： 数独输入的规则：每行每列，每个3*3的范围内不能有重复。 直接验证就可以了。
使用辅助数组bool[9]分别对：
1、对每行判断是否有重复
2、对每列判断是否有重复
3、对每个3*3判断是否有重复






实现代码：

public class Solution {
   public bool IsValidSudoku(char[,] board) 
    {
    	var row = 9;
    	var col = 9;
    	
    	// check each row
    	for(var i = 0;i < row;i ++){
    		var flag = new bool[9];;
    		for(var j = 0;j < col; j++){
    			var b = Check(board, i, j, ref flag);
    			if(!b){
    				return false;
    			}
    		}
    	}
    	
    	// check each column
    	for(var i = 0;i < col;i ++){
    		var flag = new bool[9];;
    		for(var j = 0;j < row; j++){
    			var b = Check(board, j, i, ref flag);
    			if(!b){
    				return false;
    			}
    		}
    	}
    	
    	// check each 3*3
    	for(var i = 0;i < 7; i += 3){
    		for(var j = 0;j < 7; j += 3){
    			if(!Check_3_3(board, i, j)){
    				return false;
    			}
    		}
    	}
    	
    	return true;
    }
    
    private bool Check_3_3(char[,] board, int i , int j)
    {
    	var flag = new bool[9];
    	for(var r = i; r < i + 3; r++){
    		for(var c = j; c < j + 3; c++){
    			var b = Check(board, r, c, ref flag);
    			if(!b){
    				return false;
    			}
    		}
    	}
    	
    	return true;
    }
    
    private bool Check(char[,] board, int i, int j, ref bool[] flag)
    {
    	//Console.WriteLine(i +","+j);
    	if(board[i,j] != '.'){
    		if(flag[N(board[i,j])]){
    			return false;
    		}
    		flag[N(board[i,j])] = true;	
    	}
    	
    	return true;
    }
    
    private int N(char c)
    {
    	return c - '1';
    }
}