solves 3 sum

Author: anishLearnsToCode

README.md

@@ -23,6 +23,7 @@
 |  12  | [Integer to Roman](https://leetcode.com/problems/integer-to-roman)                                                                                        |                                                                 [![Java](assets/java.png)](src/IntegerToRoman.java)                                                                  |                                                                                                                                   |
 |  13  | [Roman To Integer](https://leetcode.com/problems/roman-to-integer/)                                                                                       |                                    [![Java](assets/java.png)](src/RomanToInteger.java) [![Python](assets/python.png)](python/roman_to_integer.py)                                    | [![java-yt](assets/java-yt.png)](https://youtu.be/BCue_mO_81A) [![python-yt](assets/python-yt.png)](https://youtu.be/8h_yGTNvKMA) |
 |  14  | [Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)                                                                             |                               [![Java](assets/java.png)](src/LongestCommonPrefix.java) [![Python](assets/python.png)](python/longest_common_prefix.py)                               |                                                                                                                                   |
+|  15  | [3Sum](https://leetcode.com/problems/3sum)                                                                                                                |                                                                    [![Java](assets/java.png)](src/ThreeSum.java)                                                                     |                                                                                                                                   |
 |  20  | [ValidParentheses](https://leetcode.com/problems/valid-parentheses/)                                                                                      |                                  [![Java](assets/java.png)](src/ValidParentheses.java) [![Python](assets/python.png)](python/valid_parentheses.py)                                   |                                                                                                                                   |
 |  21  | [Merge 2 Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)                                                                             |                                [![Java](assets/java.png)](src/Merge2SortedLists.java) [![Python](assets/python.png)](python/merge_2_sorted_lists.py)                                 |                                                                                                                                   |
 |  26  | [Remove Duplicates From Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)                                                 |                  [![Java](assets/java.png)](src/RemoveDuplicatesFromSortedArray.java) [![Python](assets/python.png)](python/remove_duplicates_from_sorted_array.py)                  |                                                                                                                                   |

src/ThreeSum.java

@@ -0,0 +1,25 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public class ThreeSum {
+    public  List<List<Integer>> threeSum(int[] nums) {
+        if (nums.length < 3) return Collections.emptyList();
+        final Set<List<Integer>> triplets = new HashSet<>();
+        Arrays.sort(nums);
+
+        for (int i = 0; i < nums.length - 2; i++) {
+            for (int j = i + 1, k = nums.length - 1 ; j < k ; ) {
+                int sum = nums[i] + nums[j] + nums[k];
+                if (sum == 0) triplets.add(List.of(nums[i], nums[j++], nums[k--]));
+                else if (sum > 0) k--;
+                else j++;
+            }
+        }
+
+        return new ArrayList<>(triplets);
+    }
+}