Added task 2150.

Author: AryamanMishra

src/main/java/g2101_2200/s2150_find_all_lonely_numbers_in_the_array/Solution.java

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+package g2101_2200.s2150_find_all_lonely_numbers_in_the_array;
+
+// #Medium #Array #Hash_Table #Counting #2022_05_31_Time_93_ms_(70.66%)_Space_63.5_MB_(80.52%)
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+public class Solution {
+    public List<Integer> findLonely(int[] nums) {
+        List<Integer> ans = new ArrayList<>();
+        HashMap<Integer, Integer> m = new HashMap<>();
+        for (int i : nums) {
+            m.put(i, m.getOrDefault(i, 0) + 1);
+        }
+        for (int i : nums) {
+            if (m.get(i) == 1 && !m.containsKey(i - 1) && !m.containsKey(i + 1)) {
+                ans.add(i);
+            }
+        }
+        return ans;
+    }
+}

src/main/java/g2101_2200/s2150_find_all_lonely_numbers_in_the_array/readme.md

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+2150\. Find All Lonely Numbers in the Array
+
+Medium
+
+You are given an integer array `nums`. A number `x` is **lonely** when it appears only **once**, and no **adjacent** numbers (i.e. `x + 1` and `x - 1)` appear in the array.
+
+Return _**all** lonely numbers in_ `nums`. You may return the answer in **any order**.
+
+**Example 1:**
+
+**Input:** nums = [10,6,5,8]
+
+**Output:** [10,8]
+
+**Explanation:**
+
+- 10 is a lonely number since it appears exactly once and 9 and 11 does not appear in nums. 
+
+- 8 is a lonely number since it appears exactly once and 7 and 9 does not appear in nums. 
+
+- 5 is not a lonely number since 6 appears in nums and vice versa. 
+
+Hence, the lonely numbers in nums are [10, 8]. 
+
+Note that [8, 10] may also be returned. 
+
+**Example 2:**
+
+**Input:** nums = [1,3,5,3]
+
+**Output:** [1,5]
+
+**Explanation:**
+
+- 1 is a lonely number since it appears exactly once and 0 and 2 does not appear in nums. 
+
+- 5 is a lonely number since it appears exactly once and 4 and 6 does not appear in nums. 
+
+- 3 is not a lonely number since it appears twice. 
+
+Hence, the lonely numbers in nums are [1, 5]. 
+
+Note that [5, 1] may also be returned. 
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>5</sup></code>
+*   <code>0 <= nums[i] <= 10<sup>6</sup></code>

src/test/java/g2101_2200/s2150_find_all_lonely_numbers_in_the_array/SolutionTest.java

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+package g2101_2200.s2150_find_all_lonely_numbers_in_the_array;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import java.util.Arrays;
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void findLonely() {
+        assertThat(
+                new Solution().findLonely(new int[] {10, 6, 5, 8}), equalTo(Arrays.asList(10, 8)));
+    }
+
+    @Test
+    void findLonely2() {
+        assertThat(new Solution().findLonely(new int[] {1, 3, 5, 3}), equalTo(Arrays.asList(1, 5)));
+    }
+}