LeetCode 215. 数组中的第K个最大元素

小根堆

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        priority_queue<int,vector<int>,greater<int>> q;
        for(auto x:nums)
        {
            if(q.size()<k)
                q.push(x);
            else if(q.top()<x)
            {
                q.pop();
                q.push(x);   
            }
        }
        return q.top();
    }
};

大根堆

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        priority_queue<int,vector<int>> q;
        for(auto x:nums)
            q.push(x);
        int t=k-1;
        while(t--)
            q.pop();
        return q.top();
    }
};

快速排序

class Solution {
public:
    int quick(vector<int>& q, int k,int l,int r)
    {
        if(l==r) return q[r];
        int x=q[(l+r)>>1];
        int i=l-1,j=r+1;
        while(i<j)
        {
            do i++;while(q[i]<x);
            do j--;while(q[j]>x);
            if(i<j) swap(q[i],q[j]);
        }
        int cnt=j-l+1;
        if(k<=cnt)//答案在左边
            return quick(q,k,l,j);
        else return quick(q,k-cnt,j+1,r);   
    }
    int findKthLargest(vector<int>& nums, int k) {
        return quick(nums,nums.size()-k+1,0,nums.size()-1);
    }
};