LeetCode347. Top K Frequent Elements

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一、题目

Given an integer array nums and an integer k, return the k most frequent elements. You may return the answer in any order.

Example 1:

Input: nums = [1,1,1,2,2,3], k = 2
Output: [1,2]
Example 2:

Input: nums = [1], k = 1
Output: [1]

Constraints:

1 <= nums.length <= 105
-104 <= nums[i] <= 104
k is in the range [1, the number of unique elements in the array].
It is guaranteed that the answer is unique.

Follow up: Your algorithm’s time complexity must be better than O(n log n), where n is the array’s size.

二、题解

class Solution {
public:vector<int> topKFrequent(vector<int>& nums, int k) {unordered_map<int,int> map;priority_queue<pair<int,int>> q;for(auto x:nums){map[x]++;}for(auto it = map.begin();it != map.end();it++){q.push({it->second,it->first});}vector<int> res;while(!q.empty() && k){res.push_back(q.top().second);q.pop();k--;}return res;}
};

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