add 3158

Author: fishercoder1534

Diff for: paginated_contents/algorithms/4th_thousand/README.md

@@ -36,6 +36,7 @@
 | 3168 | [Minimum Number of Chairs in a Waiting Room](https://leetcode.com/problems/minimum-number-of-chairs-in-a-waiting-room/)                                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3168.java) |                                                                               | Easy       |
 | 3164 | [Find the Number of Good Pairs II](https://leetcode.com/problems/find-the-number-of-good-pairs-ii/)                                                                 | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3164.java) |                                                                               | Medium     |
 | 3162 | [Find the Number of Good Pairs I](https://leetcode.com/problems/find-the-number-of-good-pairs-i/)                                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3162.java) |                                                                               | Easy       |
+| 3158 | [Find the XOR of Numbers Which Appear Twice](https://leetcode.com/problems/find-the-xor-of-numbers-which-appear-twice/)                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3158.java) |                                                                               | Easy       |
 | 3157 | [Find the Level of Tree with Minimum Sum](https://leetcode.com/problems/find-the-level-of-tree-with-minimum-sum/)                                                   | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3157.java) |                                                                               | Medium     |BFS
 | 3142 | [Check if Grid Satisfies Conditions](https://leetcode.com/problems/check-if-grid-satisfies-conditions/)                                                             | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3142.java) |                                                                               | Easy       |
 | 3131 | [Find the Integer Added to Array I](https://leetcode.com/problems/find-the-integer-added-to-array-i/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3131.java) |                                                                               | Easy       |

Diff for: src/main/java/com/fishercoder/solutions/fourththousand/_3158.java

@@ -0,0 +1,19 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class _3158 {
+    public static class Solution1 {
+        public int duplicateNumbersXOR(int[] nums) {
+            int ans = 0;
+            Set<Integer> met = new HashSet<>();
+            for (int num : nums) {
+                if (!met.add(num)) {
+                    ans ^= num;
+                }
+            }
+            return ans;
+        }
+    }
+}