Added C++ solution for 4 and 15 (#90)

* Create _461.cpp

* refactor 461

* Create _15.cpp

* Create _4.cpp

* Update README.md

added c++ solution for 4 and 15

Author: Anshul1507

Diff for: README.md

@@ -969,7 +969,7 @@ _If you like this project, please leave me a star._ ★
 |18|[4 Sum](https://leetcode.com/problems/4sum/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_18.java)||Medium|Two Pointers
 |17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_17.java)||Medium|Backtracking
 |16|[3Sum Closest](https://leetcode.com/problems/3sum-closest/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_16.java)||Medium|Two Pointers
-|15|[3Sum](https://leetcode.com/problems/3sum/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_15.java)|[:tv:](https://www.youtube.com/watch?v=jeim_j8VdiM)|Medium|Two Pointers, Binary Search
+|15|[3Sum](https://leetcode.com/problems/3sum/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_15.java), [C++](../master/cpp/_15.cpp)|[:tv:](https://www.youtube.com/watch?v=jeim_j8VdiM)|Medium|Two Pointers, Binary Search
 |14|[Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_14.java)| [:tv:](https://www.youtube.com/watch?v=K1ps6d7YCy4)| Easy
 |13|[Roman to Integer](https://leetcode.com/problems/roman-to-integer)|[Solution](../master/src/main/java/com/fishercoder/solutions/_13.java)|  |Easy | Math, String
 |12|[Integer to Roman](https://leetcode.com/problems/integer-to-roman/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_12.java)||Medium| Math, String
@@ -980,7 +980,7 @@ _If you like this project, please leave me a star._ ★
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_7.java) | [:tv:](https://youtu.be/tm1Yrb_SfBM) |Easy | 
 |6|[ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_6.java) | |Easy | 
 |5|[Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_5.java) | |Medium|
-|4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_4.java) | |Hard | Divide and Conquer
+|4|[Median of Two Sorted Arrays](https://leetcode.com/problems/median-of-two-sorted-arrays/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_4.java), [C++](../master/cpp/_4.cpp) | |Hard | Divide and Conquer
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_3.java) |  |Medium | HashMap, Sliding Window
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_2.java) | |Medium | LinkedList
 |1|[Two Sum](https://leetcode.com/problems/two-sum/)|[Java](../master/src/main/java/com/fishercoder/solutions/_1.java), [C++](../master/cpp/_1.cpp), [Javascript](../master/javascript/_1.js)|[:tv:](https://www.youtube.com/watch?v=kPXOr6pW8KM&t=)|Easy| HashMap 

Diff for: cpp/_15.cpp

@@ -0,0 +1,40 @@
+class Solution {
+public:
+    vector<vector<int>> threeSum(vector<int>& nums) {
+        sort(nums.begin(),nums.end());
+        
+        vector<vector<int>> v;
+        
+        if(nums.size()<3){
+            //if vector nums has less than 3 elements, impossible to distribute into 3 element set -> return 0.
+            return v;
+        }
+        
+        for(int i=0;i<nums.size();i++){
+            
+            if(i>0 and nums[i]==nums[i-1]){
+                //same elements dont have to be taken.
+                continue;
+            }
+            
+            int l = i+1, r = nums.size()-1;
+            //Using 2-pointer concept
+            while(l<r){
+                int sum = nums[i] + nums[l] + nums[r];
+                if(sum>0){
+                    r--;
+                }else if(sum<0){
+                    l++;
+                }else{
+                    v.push_back(vector<int> {nums[i],nums[l],nums[r]});
+                    while(l<r and nums[l]==nums[l+1]) l++;
+                    while(l<r and nums[r]==nums[r-1]) r--;
+                    l++; r--;
+                }
+            }
+            
+        }
+        
+        return v;
+    }
+};

Diff for: cpp/_4.cpp

@@ -0,0 +1,18 @@
+class Solution {
+public:
+    double findMedianSortedArrays(vector<int>& nums1, vector<int>& nums2) {
+        //for adding second vector to last of first vector
+        nums1.insert(nums1.end(),nums2.begin(),nums2.end());
+        sort(nums1.begin(),nums1.end());
+        
+        int size = nums1.size();
+        float sum = nums1[size/2];
+        
+        if(size%2==0){
+            sum += nums1[(size/2)-1];
+            sum/=2;
+        }
+        
+        return (float)(sum);
+    }
+};