Valid Sudoku

来源：Leetcode

原帖：http://oj.leetcode.com/problems/valid-sudoku/

题目：
Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules (http://sudoku.com.au/TheRules.aspx). The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

代码：

 class Solution {  
 public:  
   bool isValidSudoku(vector<vector<char>> &board) {  
     const int N = 9;  
     vector<int> col(N, 0), box(N, 0);  
     for (int i = 0; i < N; ++i) { // row traverse   
       int row = 0; // update row bit  
       for (int j = 0; j < N; ++j) { // col traverse  
         if (board[i][j] == '.') continue;  
         int bit = 1 << (board[i][j] - '1');  
         int box_index = i/3*3 + j/3;  
         if ((row & bit) || (col[j] & bit) || (box[box_index] & bit)) {  
           return false;            
         }          
         row |= bit;  
         col[j] |= bit;  
         box[box_index] |= bit;  
       }  
     }  
     return true;  
   }  
 };