leetcode -- 215. Kth Largest Element in an Array

题目描述

题目难度：Medium
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.

AC代码

利用快速排序的思路

class Solution {
    public int findKthLargest(int[] nums, int k) {
        if(nums == null || nums.length == 0) return -1;
        return quickSort(nums, k , 0, nums.length - 1);
    }
    
    private int quickSort(int[] nums, int k, int start, int end){
        int tmp = nums[start];
        int low = start, high = end;
        while(low < high){
            while(low < high && nums[high] >= tmp) high--;
            if(low < high) nums[low] = nums[high];
            while(low < high && nums[low] <= tmp) low++;
            if(low < high) nums[high] = nums[low];
        }
        nums[low] = tmp;
        if(low == nums.length - k) return tmp;
        else if(low < nums.length - k) return quickSort(nums, k, low + 1, end);
        else return quickSort(nums, k, start, low - 1);
    }
}