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.

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.

解题思路：
从大到小，快速排序，返回第 k-1 个数

class Solution(object):
    def findKthLargest(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: int
        """
        l, h = 0,len(nums)-1
        self.quicksort(nums,l,h)
        return nums[k - 1]

    def quicksort(self,nums,l,h):
        if l < h:
            pivotpos = self.partition(nums,l,h)
            self.quicksort(nums,l,pivotpos - 1)
            self.quicksort(nums,pivotpos + 1,h)

    def partition(self,nums,l,h):
        p = nums[l]
        while l < h:
            while l < h and nums[h] <= p:
                h -= 1
            nums[l] = nums[h]
            while l < h and nums[l] >= p:
                l += 1
            nums[h] = nums[l]
        nums[l] = p
        return l

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