LeetCode Valid Sudoku

36. 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 ‘.’.

方法

本题实际上一共分为3种情况：按行，按列，按3 * 3块。对于3 * 3块，使用从左往右，从上往下的方式扫描。行列块分别用3个HashSet进行存放，若其hashSet有新插入的值，则返回false。

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        for(int i = 0; i < board.length; i++){
            HashSet<Character> row = new HashSet<Character>();
            HashSet<Character> col = new HashSet<Character>();
            HashSet<Character> cube = new HashSet<Character>();
            for(int j = 0; j < board[0].length; j++){
                if(board[i][j] != '.' && !row.add(board[i][j])){
                    return false;
                }
                if(board[j][i] != '.' && !col.add(board[j][i])){
                    return false;
                }
                int rowIndex = 3*(i/3);
                int colIndex = 3*(i%3);
                if(board[rowIndex+j/3][colIndex+j%3] != '.' && !cube.add(board[rowIndex+j/3][colIndex+j%3]) ){
                    return false;
                }
            }
        }
        return true;
    }
}