215-1

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        int kn = nums.size()-k;
        return quickselect(0, nums.size()-1, kn, nums);
    }

    int quickselect(int left, int right, int k, vector<int>& num){
        if(left == right) return num[left];
        int pivot = left;
        int split = partition(left, right, pivot, num);

        if(k == split)
            return num[k];
        else if(k < split)
            return quickselect(left, split-1, k, num);
        else
            return quickselect(split+1, right, k, num);
    }

    int partition(int left, int right, int pivot, vector<int>& num){
        while(left<right){
            while(left < num.size() && num[left] <= num[pivot])
                left++;
            while(num[right] > num[pivot])
                right--;
            if(left<right)
                swap(num[left], num[right]);
            else
                swap(num[pivot], num[right]);
        }
        return right;
    }
};