🚀 18-Jul-2020

Author: sureshmangs

competitive programming/leetcode/2020-July-Challenge/Day-17-Top K Frequent Elements.cpp

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+Given a non-empty array of integers, return the k most frequent elements.
+
+Example 1:
+
+Input: nums = [1,1,1,2,2,3], k = 2
+Output: [1,2]
+Example 2:
+
+Input: nums = [1], k = 1
+Output: [1]
+Note:
+
+You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
+Your algorithm's time complexity must be better than O(n log n), where n is the array's size.
+It's guaranteed that the answer is unique, in other words the set of the top k frequent elements is unique.
+You can return the answer in any order.
+
+
+
+
+
+
+
+
+
+class Solution {
+public:
+    vector<int> topKFrequent(vector<int>& nums, int k) {
+        vector<int>res;
+        priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> >   > pq; // min heap
+        unordered_map<int, int> m;
+        int n=nums.size();
+        for(int i=0;i<n;i++){
+            if(m.find(nums[i])!=m.end())
+                m[nums[i]]++;
+            else m.insert({nums[i], 1});
+        }
+        for(auto it=m.begin(); it!=m.end(); it++){
+            pq.push({it->second, it->first});
+            if(pq.size()>k) pq.pop();
+        }
+
+        while(!pq.empty()){
+            res.push_back(pq.top().second);
+            pq.pop();
+        }
+        reverse(res.begin(), res.end());
+        return res;
+    }
+};