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36. Valid Sudoku
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‎src/leetcode/_36_/Main.java

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package leetcode._36_;
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/**
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* Created by zhangbo54 on 2019-03-04.
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*/
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public class Main {
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public static void main(String[] args) {
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Solution solution = new Solution();
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char charArray[][] = {
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{'5', '3', '.', '.', '7', '.', '.', '.', '.'},
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{'6', '.', '.', '1', '9', '5', '.', '.', '.'},
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{'.', '9', '8', '.', '.', '.', '.', '6', '.'},
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{'8', '.', '.', '.', '6', '.', '.', '.', '3'},
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{'4', '.', '.', '8', '.', '3', '.', '.', '1'},
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{'7', '.', '.', '.', '2', '.', '.', '.', '6'},
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{'.', '6', '.', '.', '.', '.', '2', '8', '.'},
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{'.', '.', '.', '4', '1', '9', '.', '.', '5'},
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{'.', '.', '.', '.', '8', '.', '.', '7', '9'}};
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System.out.println(solution.isValidSudoku(charArray));
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}
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}
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‎src/leetcode/_36_/Solution.java

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package leetcode._36_;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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class Solution {
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public boolean isValidSudoku(char[][] board) {
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List<Set<Character>> hList = new ArrayList<>(27);
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List<Set<Character>> vList = new ArrayList<>(27);
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for (int i = 0; i < 27; i++) {
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hList.add(new HashSet<>());
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vList.add(new HashSet<>());
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}
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for (int i = 0; i < board.length; i++) {
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for (int j = 0; j < board[i].length; j++) {
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int vIndex = i + j / 3 * 9;
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int hIndex = j + i / 3 * 9;
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if (board[i][j] != '.') {
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if (hList.get(hIndex).contains(board[i][j]) || vList.get(vIndex).contains(board[i][j])) {
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return false;
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}
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hList.get(hIndex).add(board[i][j]);
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vList.get(vIndex).add(board[i][j]);
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}
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}
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}
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for (int i = 0; i < 9; i++) {
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// every row
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Set<Character> set = new HashSet<>();
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set.addAll(vList.get(i));
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set.addAll(vList.get(i + 9));
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set.addAll(vList.get(i + 9 * 2));
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if (set.size() != (vList.get(i).size() + vList.get(i + 9).size() + vList.get(i + 9 * 2).size())) {
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return false;
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}
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// every columns
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Set<Character> set2 = new HashSet<>();
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set2.addAll(hList.get(i));
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set2.addAll(hList.get(i + 9));
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set2.addAll(hList.get(i + 9 * 2));
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if (set2.size() != (hList.get(i).size() + hList.get(i + 9).size() + hList.get(i + 9 * 2).size())) {
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return false;
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}
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// every little 9 grips
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Set<Character> set3 = new HashSet<>();
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set3.addAll(vList.get(i * 3));
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set3.addAll(vList.get(i * 3 + 1));
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set3.addAll(vList.get(i * 3 + 2));
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if (set3.size() != (vList.get(i * 3).size() + vList.get(i * 3 + 1).size() + vList.get(i * 3 + 2).size())) {
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return false;
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}
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}
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return true;
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}
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}

‎src/leetcode/_36_/solution.md

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### [36\. Valid SudokuCopy for Markdown](https://leetcode.com/problems/valid-sudoku/)
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Difficulty: **Medium**
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Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated **according to the following rules**:
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1. Each row must contain the digits `1-9` without repetition.
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2. Each column must contain the digits `1-9` without repetition.
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3. Each of the 9 `3x3` sub-boxes of the grid must contain the digits `1-9` without repetition.
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![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)
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<small style="display: inline;">A partially filled sudoku which is valid.</small>
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The Sudoku board could be partially filled, where empty cells are filled with the character `'.'`.
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**Example 1:**
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```
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Input:
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[
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["5","3",".",".","7",".",".",".","."],
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["6",".",".","1","9","5",".",".","."],
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[".","9","8",".",".",".",".","6","."],
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["8",".",".",".","6",".",".",".","3"],
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["4",".",".","8",".","3",".",".","1"],
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["7",".",".",".","2",".",".",".","6"],
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[".","6",".",".",".",".","2","8","."],
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[".",".",".","4","1","9",".",".","5"],
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[".",".",".",".","8",".",".","7","9"]
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]
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Output: true
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```
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**Example 2:**
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```
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Input:
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[
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  ["8","3",".",".","7",".",".",".","."],
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  ["6",".",".","1","9","5",".",".","."],
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  [".","9","8",".",".",".",".","6","."],
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  ["8",".",".",".","6",".",".",".","3"],
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  ["4",".",".","8",".","3",".",".","1"],
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  ["7",".",".",".","2",".",".",".","6"],
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  [".","6",".",".",".",".","2","8","."],
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  [".",".",".","4","1","9",".",".","5"],
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  [".",".",".",".","8",".",".","7","9"]
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]
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Output: false
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Explanation: Same as Example 1, except with the 5 in the top left corner being
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modified to 8\. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
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```
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**Note:**
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* A Sudoku board (partially filled) could be valid but is not necessarily solvable.
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* Only the filled cells need to be validated according to the mentioned rules.
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* The given board contain only digits `1-9` and the character `'.'`.
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* The given board size is always `9x9`.
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#### Solution
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Language: **Java**
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```java
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      }
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       for (int i = 0; i < 9; i++) {
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           // every row
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           Set<Character> set = new HashSet<>();
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           set.addAll(vList.get(i));
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           set.addAll(vList.get(i + 9));
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           set.addAll(vList.get(i + 9 * 2));
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           if (set.size() != (vList.get(i).size() + vList.get(i + 9).size() + vList.get(i + 9 * 2).size())) {
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               return false;
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          }
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​
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           // every columns
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           Set<Character> set2 = new HashSet<>();
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           set2.addAll(hList.get(i));
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           set2.addAll(hList.get(i + 9));
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           set2.addAll(hList.get(i + 9 * 2));
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           if (set2.size() != (hList.get(i).size() + hList.get(i + 9).size() + hList.get(i + 9 * 2).size())) {
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               return false;
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          }
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​
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           // every little 9 grips
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           Set<Character> set3 = new HashSet<>();
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           set3.addAll(vList.get(i * 3));
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           set3.addAll(vList.get(i * 3 + 1));
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           set3.addAll(vList.get(i * 3 + 2));
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           if (set3.size() != (vList.get(i * 3).size() + vList.get(i * 3 + 1).size() + vList.get(i * 3 + 2).size())) {
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               return false;
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          }
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​
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      }
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       return true;
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  }
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}
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​
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```
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![](https://ws3.sinaimg.cn/large/006tKfTcgy1g1ajb5r7onj30xk0u0gql.jpg)

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