数组-Kth Largest Element in an Array（找出第K大的数）

题目描述；

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.

思考：

找出第k大的数，那就是第N-k+1小的数了，采用快速排序，时间复杂程度为O(nlogN)

代码：

public class Solution {

public static int findKthLargest(int[] nums, int k) {

int n = nums.length;
int site = n - k + 1;

if(n == 0){
return 0;
}

return find(nums, site - 1, 0, n - 1);
}

public static int find(int[] nums, int site, int left, int right){
int res = 0;

if(left <= right){
int base = nums[left];
int l = left;
int r = right;

while(l < r){
while(nums[r] >= base && l < r){

r--;
}
if(l < r){
nums[l] = nums[r];
l++;
}
while(nums[l] <= base && l < r){
l++;
}
if(l < r){
nums[r] = nums[l];
r--;
}
}

nums[r] = base;
if(r == site){
res = base;
}

else if(r> site){
int left1 = left;
int right1 = r -1;
res = find(nums, site, left1, right1);
}
else{
int left2 = r + 1;
int right2 = right;
res = find(nums, site, left2, right2);
}
}

return res;
}
}