Kth Largest Element in an Array

最新推荐文章于 2024-09-09 23:55:06 发布

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本文介绍了一种类似于快速排序的分区方法来解决在一个无序数组中寻找第K大的元素的问题。这种方法关注于从数组末尾开始进行分区，并通过不断的迭代找到目标元素的位置。

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.

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

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Silu: Just like quick sort, using the partition method.

We need to pay more attention on the partition should from end first.

public class Solution {
    public int findKthLargest(int[] nums, int k) {
        if(k>nums.length) return 0;
        int cur = 0, start = 0, end = nums.length - 1;
        while(start <= end){
            cur = pivot(nums, start, end);
            if(cur == k - 1)
                return nums[cur];
            else if(cur > (k - 1)){
                end = cur - 1;
            }else{
                start = cur + 1;
            }
        }
        return 0;
    }
    
	public int pivot(int[] nums,int start,int end){
		int t = nums[start];
		while(start<end){
			while(start<end&&nums[end]<=t){
				end--;
			}
			nums[start] = nums[end];
			while(start<end&&nums[start]>=t){
				start++;
			}
			nums[end] = nums[start];
		}
		nums[start] = t;
		return start;
	}
}