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.

利用分治算法，随机取数组中一个元素v,将数组分为三部分：小于ｖ的数，等于ｖ的数，大于ｖ的数．通过比较ｋ于这些子集所含元素数大小的关系，确定第ｋ大数在哪个子集中．对该子集递归的分治．

class Solution {public:    int findKthLargest(vector<int>& nums, int k) {int r= rand()%nums.size();int v=nums[r];    vector<int> Sl,Sv,Sr;    for (int i = 0; i < nums.size(); ++i) {    if (nums[i] > v) Sl.push_back(nums[i]);    if (nums[i] == v) Sv.push_back(nums[i]);    if (nums[i] < v) Sr.push_back(nums[i]);    }    if (k <= Sl.size()) return findKthLargest(Sl,k);    else if (k> Sl.size() && k <= Sl.size()+Sv.size()) return v;    else return findKthLargest(Sr,k-Sl.size()-Sv.size());    }};