215. Kth Largest Element in an Array

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        int left = 0, right = nums.size() - 1;
        while (true) {
            int p = partition(nums, left, right);
            if (p == k-1)
                return nums[p];
            if (p > k-1) 
                right = p - 1;
            else 
                left = p + 1;
        }
        return -1;
    }
    int partition(vector<int>& nums, int left, int right) {
        int p = nums[left];
        int i = left + 1, j = right;
        while (i <= j) {
            if (nums[i] < p && nums[j] > p) {
                swap(nums[i], nums[j]);
                i++;
                j--;
            }
            else if (nums[i] >= p)
                i++;
            else if (nums[j] <= p)
                j--;
        }
        swap(nums[left], nums[j]);
        return j;
    }
};