215. 数组中的第K个最大元素

思路1：小顶堆

class Solution {
public:
    int findKthLargest(vector& nums, int k) {

        priority_queue, greater> q;

        for(int i=0;iq.top())
                {
                    q.pop();
                    q.push(nums[i]);
                }
            }

        }

        return q.top();
    }
};

思路2：快速选择
快排的基础上改进

class Solution {
public:
    int findKthLargest(vector& nums, int k) {

        int N=nums.size();
        int target=k-1; //第k大就是N-k小
        int l=0,r=N-1;

        while(l<=r)
        {
            int mid=partition(nums,l,r);
            if(mid==target)
                return nums[mid];
            else if(mid& nums, int left, int right)
    {

        int pivot=nums[left];

        while(left=pivot && left