LeetCode 36. Valid Sudoku

题目：

确定9x9数独板是否有效。只需要根据以下规则验证填充的单元格:

1）每一行必须包含数字1-9，不能重复；

2）每一列必须包含数字1-9，不能重复；

3）网格的9个3x3子框中的每一个都必须包含数字1-9，不能重复。

【注】数独板(部分填充)可能是有效的，但不一定是可解的。只需要根据上述规则验证填充的单元格。

即检查：

1）每行是否有重复

2）每列是否有重复

3）每个3×3的小格子中是否有重复

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

A partially filled sudoku which is valid.  The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

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"]
]
Output: true

Input:
[
  ["8","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"]
]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being 
    modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.
• The given board contain only digits 1-9 and the character '.'.
• The given board size is always 9x9.

 

方法：

分别用三个函数检查三个方面

（时间上有点慢。。估计不太行=-= 可以参考下其他小可爱的~）

 

代码：

class Solution {
    public boolean isValidSudoku(char[][] board) {
        return isValidRow(board) && isValidCol(board) && isValidBox(board); 
    }

    // 行是否有重复元素或非法元素
    public boolean isValidRow(char[][] board) {
        int m = board.length;
        int n = board[0].length;
        Set<Character> set = new HashSet<Character>();
        
        for(int i=0;i<m;i++) {
            int count = 0;
            set.removeAll(set);
            for(int j=0;j<n;j++) {
                char curChar = board[i][j];
                if(curChar>'0' && curChar<='9') {
                    set.add(curChar);
                    count++;
                }
            }
        	
            if(count!=set.size()) {
                return false;
            }
        }
        return true;		
    }
    
    // 列是否有重复元素或非法元素
    public boolean isValidCol(char[][] board) {
        int m = board.length;
        int n = board[0].length;
        Set<Character> set = new HashSet<Character>();
        
        for(int i=0;i<m;i++) {
            int count = 0;
            set.removeAll(set);
            for(int j=0;j<n;j++) {
                char curChar = board[j][i];
                if(curChar>'0' && curChar<='9') {
                    set.add(curChar);
                    count++;
                }
            }
        	
            if(count!=set.size()) {
                return false;
            }
        }
        return true;			
    }
    
    // 3×3的格子里是否有重复
    public boolean isValidBox(char[][] board) {
        int m = board.length-1;
        int n = board[0].length-1;
        
        for(int i=0;i<m;i=i+3) {
            for(int j=0;j<n;j=j+3) {
                if(checkBox(board, i, j)==false) {
                    return false;
                }
            }
        }
        return true;   		
    }
    
    public boolean checkBox(char[][] board,int m_start, int n_start) {
        Set<Character> set = new HashSet<Character>();
        int count = 0;
        for(int i=0;i<3;i++) {
            for(int j=0;j<3;j++) {
                char curChar = board[i+m_start][j+n_start];
                if(curChar>'0' && curChar<='9') {
                    set.add(curChar);
                    count++;
                }
            }
        }
        
        if(count==set.size()) {
            return true;
        }else {
            return false;
        }
    }
}