leetcode215 Kth Largest Element in an Array-zh

# 215. 数组中的第K个最大元素 (opens new window)

# 题目描述

在未排序的数组中找到第 k 个最大的元素。请注意，你需要找的是数组排序后的第 k 个最大的元素，而不是第 k 个不同的元素。

示例 1:

输入: [3,2,1,5,6,4] 和 k = 2
输出: 5

示例 2:

输入: [3,2,3,1,2,4,5,5,6] 和 k = 4
输出: 4

说明:

你可以假设 k 总是有效的，且 1 ≤ k ≤ 数组的长度。

# 解法

快速排序 partition 实现。

# Python3

class Solution:
    def findKthLargest(self, nums: List[int], k: int) -> int:
        def quickSort(nums, left, right, k):
            if left == right:
                return nums[left]
            i, j = left - 1, right + 1
            x = nums[(left + right) >> 1]
            while i < j:
                while 1:
                    i += 1
                    if nums[i] >= x:
                        break
                while 1:
                    j -= 1
                    if nums[j] <= x:
                        break
                if i < j:
                    nums[i], nums[j] = nums[j], nums[i]
            if j < k:
                return quickSort(nums, j + 1, right, k)
            return quickSort(nums, left, j, k)

        n = len(nums)
        return quickSort(nums, 0, n - 1, n - k)

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# Java

class Solution {
    public int findKthLargest(int[] nums, int k) {
        int n = nums.length;
        return quickSort(nums, 0, n - 1, n - k);
    }

    private int quickSort(int[] nums, int left, int right, int k) {
        if (left == right) {
            return nums[left];
        }
        int i = left - 1, j = right + 1;
        int x = nums[(left + right) >>> 1];
        while (i < j) {
            while (nums[++i] < x);
            while (nums[--j] > x);
            if (i < j) {
                int t = nums[i];
                nums[i] = nums[j];
                nums[j] = t;
            }
        }
        if (j < k) {
            return quickSort(nums, j + 1, right, k);
        }
        return quickSort(nums, left, j, k);

    }
}

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# C++

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        int n = nums.size();
        return quickSort(nums, 0, n - 1, n - k);
    }

    int quickSort(vector<int>& nums, int left, int right, int k) {
        if (left == right) {
            return nums[left];
        }
        int i = left - 1, j = right + 1;
        int x = nums[left + right >> 1];
        while (i < j) {
            while (nums[++i] < x);
            while (nums[--j] > x);
            if (i < j) {
                swap(nums[i], nums[j]);
            }
        }
        if (j < k) {
            return quickSort(nums, j + 1, right, k);
        }
        return quickSort(nums, left, j, k);
    }
};

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# Go

func findKthLargest(nums []int, k int) int {
	n := len(nums)
	return quickSort(nums, 0, n-1, n-k)
}

func quickSort(nums []int, left, right, k int) int {
	if left == right {
		return nums[left]
	}
	i, j := left-1, right+1
	x := nums[(left+right)>>1]
	for i < j {
		for {
			i++
			if nums[i] >= x {
				break
			}
		}
		for {
			j--
			if nums[j] <= x {
				break
			}
		}
		if i < j {
			nums[i], nums[j] = nums[j], nums[i]
		}
	}
	if j < k {
		return quickSort(nums, j+1, right, k)
	}
	return quickSort(nums, left, j, k)
}

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# ...

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上次更新: 2021/10/30, 12:58:38

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