215. 数组中的第K个最大元素 - 力扣(LeetCode)
写个快排,使数组升序,返回倒数第k个元素即可
func quickSort(nums []int, l int, r int) {if l >= r {return}x := nums[(l + r) / 2]i := l - 1j := r + 1for i < j {for {i++if nums[i] >= x {break}}for {j--if nums[j] <= x {break}}if i < j {tmp := nums[i]nums[i] = nums[j]nums[j] = tmp}}quickSort(nums, l, j)quickSort(nums, j + 1, r)
}func findKthLargest(nums []int, k int) int {quickSort(nums, 0, len(nums) - 1)return nums[len(nums) - k]
}
347. 前 K 个高频元素 - 力扣(LeetCode)
统计每个元素的出现次数,按照出现次数排序即可
class Solution {
public:vector<int> topKFrequent(vector<int>& nums, int k) {unordered_map<int, int> cnt;for (const auto t : nums) {cnt[t]++;}priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q;for (const auto t : cnt) {if (q.size() == k && q.top().first < t.second) {q.pop();}if (q.size() != k) {q.push({t.second, t.first});}}vector<int> ans;while (q.size()) {ans.push_back(q.top().second);q.pop();}return ans;}
};