leetcode 215. Kth Largest Element in an Array

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

For example,
Given [3,2,1,5,6,4] and k = 2, return 5.

Note: 
You may assume k is always valid, 1 ? k ? array's length.

求第k大的数。用小堆去维护

这题几年前做过...

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        priority_queue<int,vector<int>, greater<int>> q;
        for (int i = 0; i < nums.size(); ++i) {
            if (q.empty()) q.push(nums[i]);
            else {
                int x = q.top();
                if (q.size() < k) q.push(nums[i]);
                else {
                    if (nums[i] > x) q.pop(), q.push(nums[i]);
                }
            }
        }
        if (q.empty()) return 0;
        return q.top();
    }
};