力扣hot100——347.前K个高频元素（cpp手撕堆）

题目链接：347. 前 K 个高频元素 - 力扣（LeetCode）

cpp版手撕堆

class Solution {
public:// 向下调整堆（最小堆）void shiftDown(vector<pair<int, int>>& heap, int index,int len) {int parent = index;int child = 2 * parent + 1;while (child < len) {if (child + 1 < len && heap[child + 1].second < heap[child].second) {child++;}if (heap[parent].second > heap[child].second) {swap(heap[parent], heap[child]);parent = child;child = 2 * parent + 1;} else {break;}}}vector<int> topKFrequent(vector<int>& nums, int k) {// 统计每个数字出现的频率unordered_map<int, int> freqMap;for (int num : nums) {freqMap[num]++;}// 初始化堆，放入前 k 个元素vector<pair<int, int>> minHeap;for (const auto& entry : freqMap) {if (minHeap.size() < k) {minHeap.push_back(entry);}}// 构造一个合法的最小堆for (int i = minHeap.size() / 2 - 1; i >= 0; i--) {shiftDown(minHeap, i,k);}// 处理剩下的元素int processedCount = 0;for (const auto& entry : freqMap) {if (processedCount < k || entry.second <= minHeap[0].second) {processedCount++;continue;}minHeap[0] = entry;shiftDown(minHeap, 0,k);}// 提取结果vector<int> result;for (const auto& p : minHeap) {result.push_back(p.first);}return result;}
};