36. Valid Sudoku solution 2

Author: coderbean

src/leetcode/_36_/Solution.java

@@ -1,60 +1,23 @@
 package leetcode._36_;
 
-import java.util.ArrayList;
 import java.util.HashSet;
-import java.util.List;
 import java.util.Set;
 
 class Solution {
     public boolean isValidSudoku(char[][] board) {
-        List<Set<Character>> hList = new ArrayList<>(27);
-        List<Set<Character>> vList = new ArrayList<>(27);
-        for (int i = 0; i < 27; i++) {
-            hList.add(new HashSet<>());
-            vList.add(new HashSet<>());
-        }
-        for (int i = 0; i < board.length; i++) {
-            for (int j = 0; j < board[i].length; j++) {
-                int vIndex = i + j / 3 * 9;
-                int hIndex = j + i / 3 * 9;
-                if (board[i][j] != '.') {
-                    if (hList.get(hIndex).contains(board[i][j]) || vList.get(vIndex).contains(board[i][j])) {
+        Set<String> seen = new HashSet<>();
+        for (int i = 0; i < 9; i++) {
+            for (int j = 0; j < 9; j++) {
+                char num = board[i][j];
+                if (num != '.') {
+                    if (!seen.add(num + " in row " + i)
+                            || !seen.add(num + " in column " + j)
+                            || !seen.add(num + " in block " + i / 3 + "," + j / 3)) {
                         return false;
                     }
-                    hList.get(hIndex).add(board[i][j]);
-                    vList.get(vIndex).add(board[i][j]);
                 }
             }
         }
-        for (int i = 0; i < 9; i++) {
-            // every row
-            Set<Character> set = new HashSet<>();
-            set.addAll(vList.get(i));
-            set.addAll(vList.get(i + 9));
-            set.addAll(vList.get(i + 9 * 2));
-            if (set.size() != (vList.get(i).size() + vList.get(i + 9).size() + vList.get(i + 9 * 2).size())) {
-                return false;
-            }
-
-            // every columns
-            Set<Character> set2 = new HashSet<>();
-            set2.addAll(hList.get(i));
-            set2.addAll(hList.get(i + 9));
-            set2.addAll(hList.get(i + 9 * 2));
-            if (set2.size() != (hList.get(i).size() + hList.get(i + 9).size() + hList.get(i + 9 * 2).size())) {
-                return false;
-            }
-
-            // every little 9 grips
-            Set<Character> set3 = new HashSet<>();
-            set3.addAll(vList.get(i * 3));
-            set3.addAll(vList.get(i * 3 + 1));
-            set3.addAll(vList.get(i * 3 + 2));
-            if (set3.size() != (vList.get(i * 3).size() + vList.get(i * 3 + 1).size() + vList.get(i * 3 + 2).size())) {
-                return false;
-            }
-
-        }
         return true;
     }
 }

src/leetcode/_36_/solution2.md

@@ -0,0 +1,88 @@
+### [36\. Valid SudokuCopy for MarkdownCopy for MarkdownCopy for Markdown](https://leetcode.com/problems/valid-sudoku/)
+
+Difficulty: **Medium**
+
+
+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.
+
+![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png)  
+<small style="display: inline;">A partially filled sudoku which is valid.</small>
+
+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`.
+
+
+#### Solution
+
+Language: **Java**
+
+```java
+class Solution {
+    public boolean isValidSudoku(char[][] board) {
+        Set<String> seen = new HashSet<>();
+        for (int i = 0; i < 9; i++) {
+            for (int j = 0; j < 9; j++) {
+                char num = board[i][j];
+                if (num != '.') {
+                    if (!seen.add(num + " in row " + i)
+                            || !seen.add(num + " in column " + j)
+                            || !seen.add(num + " in block " + i / 3 + "," + j / 3)) {
+                        return false;
+                    }
+                }
+            }
+        }
+        return true;
+    }
+}
+​
+```
+![](https://ws1.sinaimg.cn/large/006tKfTcgy1g1ajv1n01vj30zo0lc77f.jpg)