https://leetcode.com/problems/kth-largest-element-in-an-array/description/
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
class Solution {
public:
int findKthLargest(vector<int>& nums, int k) {
int left = 0, right = nums.size() - 1;
while (true) {
int pos = partition(nums, left, right);
if (pos == k - 1) return nums[pos];
else if (pos > k - 1) right = pos - 1;
else left = pos + 1;
}
}
//利用了快排的思路，pivot在正确的位置上
int partition(vector<int>& nums, int left, int right) {
int pivot = nums[left], l = left + 1, r = right;
while (l <= r) {
if (nums[l] < pivot && nums[r] > pivot) {
swap(nums[l++], nums[r--]);
}
if (nums[l] >= pivot) ++l;
if (nums[r] <= pivot) --r;
}
swap(nums[left], nums[r]);
//退出时r 指向的永远是> pivot 的,l指向的是< pivot的
return r;
}
};
//PQ
class Solution {
public:
int findKthLargest(vector<int>& nums, int k) {
priority_queue<int> pq(nums.begin(), nums.end());
for (int i = 0; i < k - 1; i++)
pq.pop();
return pq.top();
}
};