hashset

Author: Simcoderan

36.Valid Sudoku/Medium36.java

@@ -0,0 +1,55 @@
+
+import java.util.HashSet;
+
+public class Medium36 {
+
+    public boolean isValidSudoku(char[][] board) {
+        int N = 9;
+
+       // Use hash set to record the status
+       HashSet<Character>[] rows = new HashSet[N];
+       HashSet<Character>[] cols = new HashSet[N];
+       HashSet<Character>[] boxes = new HashSet[N];
+       for (int r = 0; r < N; r++) {
+           rows[r] = new HashSet<Character>();
+           cols[r] = new HashSet<Character>();
+           boxes[r] = new HashSet<Character>();
+       }
+
+       for (int r = 0; r < N; r++) {
+           for (int c = 0; c < N; c++) {
+               char val = board[r][c];
+
+               // Check if the position is filled with number
+               if (val == '.') {
+                   continue;
+               }
+
+               // Check the row
+               if (rows[r].contains(val)) {
+                   return false;
+               }
+               rows[r].add(val);
+
+               // Check the column
+               if (cols[c].contains(val)) {
+                   return false;
+               }
+               cols[c].add(val);
+
+               // Check the box
+               int idx = (r / 3) * 3 + c / 3;
+               if (boxes[idx].contains(val)) {
+                   return false;
+               }
+               boxes[idx].add(val);
+           }
+       }
+       return true;
+
+       
+   }
+
+
+    
+}