LeetCode 215. Kth Largest Element in an Array

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.

解题思路：我采用的排序方法，然后从排序后的数组中取出对应的值就好。

public class Solution {    public int findKthLargest(int[] nums, int k) {        Arrays.sort(nums);        return nums[nums.length-k];    }}

这样的语句太简单了，就在网上找了一下分治法的解法，发现了一篇不错的博客 点击打开链接，看了之后也自己动手敲了一下。

public class Solution {    public int findKthLargest(int[] nums, int k) {       int left=0;       int right=nums.length-1;       while(true){              int pos = helper(nums,left,right);           if(pos==k-1){               return nums[pos];           }else if(pos< k-1){               left=pos+1;           }else{               right=pos-1;           }       }    }    public int helper(int[] nums,int begin ,int end ){        int left = begin +1;        int right = end;        while(left <=right){            if(nums[left]<nums[begin] && nums[right]>nums[begin]){                swap(nums,left,right);            }            if(nums[left]>=nums[begin]){                left++;            }            if(nums[right]<=nums[begin]){                right--;            }        }        swap(nums,begin,right);        return right;    }    public void swap(int[] nums, int i,int j){        int temp=nums[i];        nums[i]=nums[j];        nums[j]=temp;            }}