说明

算法： Valid Sudoku 地址：https://leetcode.com/problems/valid-sudoku/

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

Each row must contain the digits 1-9 without repetition.Each column must contain the digits 1-9 without repetition.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 ‘.’.

Example 1:

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

Example 2:

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.

解法

有效数独，也就是行，列，33方块不能有重复的数字。 最简单明了的方法，用一个HashSet来判断 行：data + “row” + rowId 列： data + “col” + colId 33方块： data + “block” + rowId/3 + “_” + colId/3

前提条件排除：data != ‘.’

public boolean isValidSudokuWithOneHashset(char[][] board) { HashSet<String> set = new HashSet<>(); char item; for (int i = 0; i < 9; i++) { for (int j = 0; j < 9; j++) { item = board[i][j]; if (item == '.') { continue; } if (!set.add(item + "row" + i)) { return false; } if (!set.add(item + "col" + j)) { return false; } if (!set.add(item + "block" + i/3 + "_" + j/3)) { return false; } } } return true; }

代码下载

https://github.com/zgpeace/awesome-java-leetcode/blob/master/code/LeetCode/src/hashtable/ValidSudoku.java