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.

Credits:

Special thanks to @mithmatt for adding this problem and creating all test cases.

我AC的做法：

class Solution:    def findKthLargest(self, nums, k):        """        :type nums: List[int]        :type k: int        :rtype: int        """

时间复杂度：O(nlogn) 因为用的是快速排序

66ms,竟然打败了74.14%的python3答案，但我相信这肯定不是这道题的考点

快速选择算法：

复杂度：时间 Avg O(N) Worst O(N^2) 空间 O(1)

 class Solution:    def findKthLargest(self, nums, k):        """        :type nums: List[int]        :type k: int        :rtype: int        """        pivot = nums[0]        left  = []        equal = []        right = []        for i in nums:            if i<pivot:                left.append(i)            elif i==pivot:                equal.append(i)            else:                right.append(i)        if k <= len(right):            return self.findKthLargest(right, k)        elif (k - len(right)) <= len(equal):            return equal[0]        else:            return self.findKthLargest(left, k - len(right) - len(equal))

思想是对的， pivot变成随机选取会比固定选数组第一个值好，但实际AC不了，因为内存溢出

最后：https://segmentfault.com/a/1190000003704825  这篇文章总结的很好