added Merge Similar Items problem

Ordered Set/Merge Similar Items.cpp

@@ -0,0 +1,26 @@
+class Solution
+{
+public:
+    vector<vector<int> > mergeSimilarItems(vector<vector<int> > &items1, vector<vector<int> > &items2)
+    {
+        map<int, int> mp;
+        for (int i = 0; i < items1.size(); i++)
+        {
+            mp[items1[i][0]] += items1[i][1];
+        }
+        for (int i = 0; i < items2.size(); i++)
+        {
+            mp[items2[i][0]] += items2[i][1];
+        }
+
+        vector<vector<int> > res;
+        for (auto it = mp.begin(); it != mp.end(); ++it)
+        {
+            vector<int> temp;
+            temp.push_back(it->first);
+            temp.push_back(it->second);
+            res.push_back(temp);
+        }
+        return res;
+    }
+};