347. 前 K 个高频元素 -- leetcode

堆排序

class Solution {
    
    
public:

    void heap_adjust(vector<pair<int,int>>& heap, int i, int n) {
    
    
        auto key = heap[i];
        int j = 2*i;

        while(j<=n){
    
    
            if(j+1 <= n && heap[j].second > heap[j+1].second) {
    
    
                j++;
            } 

            if (key.second <= heap[j].second) {
    
    
                break;
            }
            heap[j/2] = heap[j];
            j*=2;
        }
        heap[j/2] = key;
    }
    vector<int> topKFrequent(vector<int>& nums, int k) {
    
    
        unordered_map<int, int> dict;
        for(int i=0;i<nums.size();i++){
    
    
            dict[nums[i]]++;
        }
        vector<pair<int,int>> heap(1);
        for(auto it = dict.begin();it!=dict.end();it++){
    
    
            heap.push_back(*it);
        }
        int n = heap.size() - 1;
        for(int i=n/2;i>=1;i--){
    
    
            heap_adjust(heap, i, n);
        }


        for(int i=n;i>1;i--){
    
    
            swap(heap, 1, i);
            heap_adjust(heap, 1, i-1);
        }

        vector<int> res;
        for(int i=1;i<=k;i++){
    
    
            res.push_back(heap[i].first);
        }
        return res;
    }

    void swap(vector<pair<int, int>> &heap, int i, int j){
    
    
        auto temp = heap[i];
        heap[i] = heap[j];
        heap[j] = temp;
    }
};