Adding Solution to 3 Sum in C++ (#132)

* Added solution in c++ for #973

* Added name and details in Contributors

* Update README.md

* Update README.md

* Update README.md

* Update README.md

* Added Solution to 3 Sum problem in C++

* Update README.md

* Delete 3sum.cpp

* Update README.md

* Add files via upload

* Update README.md

Author: Francode007

C++/3sum.cpp

@@ -0,0 +1,51 @@
+class Solution {
+public:
+    vector<vector<int>> threeSum(vector<int>& nums) {
+        vector<vector<int> > res;
+
+    std::sort(nums.begin(), nums.end());
+
+    for (int i = 0; i < nums.size(); i++) {
+        
+        int target = -nums[i];
+        int front = i + 1;
+        int back = nums.size() - 1;
+
+        while (front < back) {
+
+            int sum = nums[front] + nums[back];
+            
+            // Finding answer which start from number nums[i]
+            if (sum < target)
+                front++;
+
+            else if (sum > target)
+                back--;
+
+            else {
+                vector<int> triplet(3, 0);
+                triplet[0] = nums[i];
+                triplet[1] = nums[front];
+                triplet[2] = nums[back];
+                res.push_back(triplet);
+                
+                // Processing duplicates of Number 2
+                // Rolling the front pointer to the next different number forwards
+                while (front < back && nums[front] == triplet[1]) front++;
+
+                // Processing duplicates of Number 3
+                // Rolling the back pointer to the next different number backwards
+                while (front < back && nums[back] == triplet[2]) back--;
+            }
+            
+        }
+
+        // Processing duplicates of Number i
+        while (i + 1 < nums.size() && nums[i + 1] == nums[i]) 
+            i++;
+
+    }
+    
+    return res;
+    }
+};

README.md

@@ -267,6 +267,8 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 005 | [Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [Python](./Python/5_LongestPalindromicSubstring.py) <br> [JavaScript](./JavaScript/5.Longest-Palindromic-Substring.js) | _O(N^2)_ <br> _O(N^2)_ | _O(N)_ <br> _O(1)_ | Medium     |             | Expand the Wings |
 | 4   | [Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)     | [Java](./Java/median-of-two-sorted-arrays.java)                                                                        | _O(log(min(m,n)))_     | _O(1)_             | Hard       |             |                  |
 | 845 | [Longest Mountain in Array](https://leetcode.com/problems/longest-mountain-in-array/)         | [C++](./C++/Longest-Mountain-in-Array.cpp)                                                                             | _O(N)_                 | _O(1)_             | Medium     | Two Pointer |
+| 015 | [3 Sum](https://leetcode.com/problems/3sum/)                                                  | [C++](./C++/3sum.cpp)                                                                                                  | _O(N)_                 | _O(1)_             | Medium     | Two Pointer |                  |
+
 
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