add 3978

Author: fishercoder1534

paginated_contents/algorithms/4th_thousand/README.md

@@ -6,6 +6,7 @@
 | 3982 | [Sum of Integers with Maximum Digit Range](https://leetcode.com/problems/sum-of-integers-with-maximum-digit-range/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3982.java) |                                                                               | Easy       |
 | 3925 | [Concatenate Array With Reverse](https://leetcode.com/problems/concatenate-array-with-reverse/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3925.java) |                                                                               | Easy       |
 | 3908 | [Valid Digit Number](https://leetcode.com/problems/valid-digit-number/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3908.java) |                                                                               | Easy       |
+| 3978 | [Unique Middle Element](https://leetcode.com/problems/unique-middle-element/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3978.java) |                                                                               | Easy       |
 | 3502 | [Minimum Cost to Reach Every Position](https://leetcode.com/problems/minimum-cost-to-reach-every-position/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3502.java) |                                                                               | Easy       |
 | 3491 | [Phone Number Prefix](https://leetcode.com/problems/phone-number-prefix/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3491.java) |                                                                               | Easy       |
 | 3477 | [Fruits Into Baskets II](https://leetcode.com/problems/fruits-into-baskets-ii/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3477.java) |                                                                               | Easy       |

src/main/java/com/fishercoder/solutions/fourththousand/_3978.java

@@ -0,0 +1,16 @@
+package com.fishercoder.solutions.fourththousand;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class _3978 {
+    public static class Solution1 {
+        public boolean isMiddleElementUnique(int[] nums) {
+            Map<Integer, Integer> map = new HashMap<>();
+            for (int num : nums) {
+                map.put(num, map.getOrDefault(num, 0) + 1);
+            }
+            return map.get(nums[(nums.length - 1) / 2]) == 1;
+        }
+    }
+}