Created k_freq_words.cpp

692. Top K Frequent Words/k_freq_words.cpp

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+
+class Solution {
+public:
+    vector<string> topKFrequent(vector<string>& words, int k) {
+        unordered_map<string, int> hashmap;
+        for(string& word : words) {
+            hashmap[word] += 1;
+        }
+        priority_queue<pair<int, string>, vector<pair<int, string>>, MyComp> pq;
+        for(auto it = hashmap.begin(); it != hashmap.end(); ++it) {
+            pq.push(make_pair(it->second, it->first));
+            if(pq.size() > k) pq.pop();
+        }
+        vector<string> res;
+        while(!pq.empty()) {
+            // res.insert(res.begin(), pq.top().second);
+            res.push_back(pq.top().second); // push the results in increasing, and reverse later
+            pq.pop();
+        }
+        reverse(res.begin(), res.end());
+        return res;
+    }
+private:
+    struct MyComp {
+        bool operator() (const pair<int, string>& a, const pair<int, string>& b) {
+            if(a.first != b.first) {
+                return a.first > b.first;
+            }
+            else {
+                return a.second < b.second;
+            }
+        }
+    };
+};
+