【LEETCODE】215-Kth Largest Element in an Array

最新推荐文章于 2020-03-01 17:17:45 发布

原创最新推荐文章于 2020-03-01 17:17:45 发布 · 643 阅读

1 ·

CC 4.0 BY-SA版权

文章标签：

#LEETCODE #PYTHON

LEETCODE 专栏收录该内容

137 篇文章

订阅专栏

本文介绍了一种使用快速选择算法解决查找未排序数组中第k大元素的问题，包括实现步骤和时间复杂度分析。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

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.

内部有sort命令，找到第k个大的

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

        return sorted(nums, reverse=True)[k - 1]

参考：

http://bookshadow.com/weblog/2015/05/23/leetcode-kth-largest-element-array/

O(n)解法：快速选择算法

import random

class Solution(object):
    def findKthLargest(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: int
        """
        
        r=random.choice(nums)
        nums1=[]                                              #存比r大的数
        nums2=[]                                              #<span style="font-family: Arial, Helvetica, sans-serif;">存比r小的数</span>

        
        for num in nums:
            if num>r:
                nums1.append(num)
            elif num<r:
                nums2.append(num)
        
        if k<=len(nums1):<span style="font-family: Arial, Helvetica, sans-serif;">                                                                            </span><span style="font-family: Arial, Helvetica, sans-serif;">       #在nums1里找第k个</span><span style="font-family: Arial, Helvetica, sans-serif;">
</span>            return self.findKthLargest(nums1,k)
        if k>len(nums)-len(nums2):                              #在nums2里找第 <span style="font-family: Arial, Helvetica, sans-serif;">k-(len(nums)-len(nums2))  个</span>
            return self.findKthLargest(nums2,k-(len(nums)-len(nums2)))
        return r