LeetCode 215 數組中的第K個最大元素

利用快速排序的方法解決

from typing import *
class Solution:
    def findKthLargest(self, nums: List[int], k: int) -> int:
        return self.helper2(nums,0,len(nums)-1,len(nums)-k+1)

    def helper2(self,nums,lo,hi,k):
        idx=self.helper1(nums,lo,hi)
        if idx-lo+1==k:
            return nums[idx]
        elif idx-lo+1>k:
            return self.helper2(nums,lo,idx-1,k)
        return self.helper2(nums,idx+1,hi,k-idx+lo-1)


    def helper1(self,nums,lo,hi):
        idx=random.randint(lo,hi)
        nums[idx],nums[hi]=nums[hi],nums[idx]
        val=nums[hi]
        i=lo-1
        for j in range(lo,hi):
            if nums[j]<val:
                i+=1
                nums[i],nums[j]=nums[j],nums[i]
        nums[i+1],nums[hi]=nums[hi],nums[i+1]
        return i+1