ADD: Group anagram - medium problem

XDaysChallenge/90DaysChallenge/Day1 - hashing/group_anagrams.cpp

@@ -0,0 +1,31 @@
+// https://leetcode.com/problems/group-anagrams/
+
+/**
+ * Should now hashing and how to use it to reduce O(N^2) complexity
+*/
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+
+        unordered_map<string, vector<string>> store;
+
+        vector<string> copyStrs = strs;
+
+        // sort all of them
+        for(int i=0;i<strs.size();i++) {
+            sort(strs[i].begin(), strs[i].end());
+        }
+
+        vector<bool> itemPicked(strs.size(), false);
+        // now compare
+        vector<vector<string>> result;
+
+        for(int i=0;i<strs.size();i++) {
+            store[strs[i]].push_back(copyStrs[i]);
+        }
+        for(auto i = store.begin();i!=store.end();i++) {
+            result.push_back(i->second);
+        }
+        return result;
+    }
+};