Create ValidSoduku.java

Java/ValidSoduku.java

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+/*
+Determine if a 9 x 9 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 nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.
+*/
+
+class Solution {
+    public boolean isValidSudoku(char[][] board) {
+    HashSet<String>seen = new HashSet<>();
+
+    for (int i = 0; i < 9; ++i)
+      for (int j = 0; j < 9; ++j) {
+        if (board[i][j] == '.')
+          continue;
+        final char c = board[i][j];
+        if (!seen.add(c + "@row" + i) ||
+            !seen.add(c + "@col" + j) ||
+            !seen.add(c + "@box" + i / 3 + j / 3))
+          return false;
+      }
+
+    return true;
+    }
+}