Added : 3 Sum

Author: rohitkumar-rk

LeetCode/Array/15. 3 Sum/Problem Statement.txt

@@ -0,0 +1,15 @@
+Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
+
+Note:
+
+The solution set must not contain duplicate triplets.
+
+Example:
+
+Given array nums = [-1, 0, 1, 2, -1, -4],
+
+A solution set is:
+[
+  [-1, 0, 1],
+  [-1, -1, 2]
+]

LeetCode/Array/15. 3 Sum/Solution.java

@@ -0,0 +1,51 @@
+/*
+@lc id : 15
+@problem : 3 Sum
+@author : rohit
+@url : https://leetcode.com/problems/3sum/
+@difficulty : medium
+*/
+
+class Solution {
+    
+    public void twoSums(int[] nums, int requiredSum, int first, List<List<Integer>>  result){
+        
+        int second = nums.length - 1;
+        
+        while(first < second){
+            
+            int currSum = nums[first] + nums[second];
+
+            if(currSum == requiredSum){
+                result.add(Arrays.asList(-requiredSum, nums[first], nums[second]));
+                first++;
+                second--;
+
+                while(nums[first] == nums[first-1] && first < second)
+                    first++;
+
+                while(nums[second] == nums[second+1] && second > first)
+                    second--;
+            }
+            
+            else if(currSum > requiredSum) second--;
+            else first++;
+
+        }
+    }
+    
+    
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+        Arrays.sort(nums);
+        
+        for(int i = 0; i < nums.length - 2; i++){
+            if(i > 0 && nums[i] == nums[i-1])
+                continue;
+            twoSums(nums, -nums[i], i+1, result);
+        }
+
+        return result;
+        
+    }
+}