11-215. Kth Largest Element in an Array

题目描述：

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.

Example 1:

Input: [3,2,1,5,6,4] and k = 2
Output: 5

Example 2:

Input: [3,2,3,1,2,4,5,5,6] and k = 4
Output: 4

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

代码：

class Solution:
    def findKthLargest(self, nums, k) -> int:
        # shuffle nums to avoid n*n
        random.shuffle(nums)
        return self.quickSelection(nums, 0, len(nums) - 1, len(nums) - k)

    def quickSelection(self, nums, start, end, k):
        if start > end:
            return float('inf')
        pivot = nums[end]
        left = start
        for i in range(start, end):
            if nums[i] <= pivot:
                # swip left and i
                nums[left], nums[i] = nums[i], nums[left]
                left += 1
        nums[left], nums[end] = nums[end], nums[left]
        if left == k:
            return nums[left]
        elif left < k:
            return self.quickSelection(nums, left + 1, end, k)
        else:
            return self.quickSelection(nums, start, left - 1, k)

一个基于python的很好的分析：https://leetcode.com/problems/kth-largest-element-in-an-array/discuss/301338/Python-or-tm-215