官方链接
https://leetcode-cn.com/problems/valid-sudoku/
判断一个 9x9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。
数字 1-9 在每一行只能出现一次。
数字 1-9 在每一列只能出现一次。
数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。
上图是一个部分填充的有效的数独。
数独部分空格内已填入了数字，空白格用 '.' 表示。
示例 1:
输入:
[
["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"]
]
输出: true示例 2:
输入:
[
["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"]
]
输出: false
解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。
但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。说明:
一个有效的数独（部分已被填充）不一定是可解的。
只需要根据以上规则，验证已经填入的数字是否有效即可。
给定数独序列只包含数字 1-9 和字符 '.' 。
给定数独永远是 9x9 形式的。解法一
哈希表
class Solution {
public boolean isValidSudoku(char[][] board) {
List<Map<Integer, Integer>> row = new ArrayList<>();
List<Map<Integer, Integer>> col = new ArrayList<>();
List<Map<Integer, Integer>> box = new ArrayList<>();
for(int i = 0; i < board.length; i++) {
row.add(new HashMap<>());
col.add(new HashMap<>());
box.add(new HashMap<>());
}
for(int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
if(board[i][j] == '.') continue;
int one = (int)board[i][j];
if (row.get(i).containsKey(one) || col.get(j).containsKey(one) || box.get((i/3) * 3 + j/3).containsKey(one)) {
return false;
} else {
row.get(i).put(one, 1);
col.get(j).put(one, 1);
box.get((i/3) * 3 + j/3).put(one, 1);
}
}
}
return true;
}
}
HashSet
class Solution {
public boolean isValidSudoku(char[][] board) {
List<Set<Integer>> cols = new ArrayList<>();
List<Set<Integer>> blocks = new ArrayList<>();
for(int i = 0; i < board.length; i++) {
cols.add(new HashSet<>());
blocks.add(new HashSet<>());
}
for(int i = 0; i < board.length; i++) {
Set<Integer> row = new HashSet<>();
for(int j = 0; j < board[i].length; j++) {
if (board[i][j] == '.') continue;
int one = (int) board[i][j];
if (row.contains(one) || cols.get(j).contains(one) || blocks.get((i/3)*3 + j/3).contains(one)) return false;
row.add(one);
cols.get(j).add(one);
blocks.get((i/3)*3 + j/3).add(one);
}
}
return true;
}
}