LeetCode Kth Largest Element in an Array

class Solution {
public:
    int findKthLargest(vector<int>& nums, int k) {
        int len = nums.size();
        
        int start = 0;
        int end = len;
        // convert to kth smallest element sematic
        k = len - k + 1;
        while (start < end) {
            int idx = partition(nums, start, end);

            if (idx == k - 1) {
                return nums[idx];
            } else if (idx < k - 1) {
                start = idx + 1;
                k = k - (idx - start + 1);
            } else {
                end = idx;
            }
        }
        return nums[start];
    }
    
    int partition(vector<int>& nums, int start, int end) {
        if (start >= end) {
            return -1;
        }
        int pv = nums[--end];
        int div = start;
        for (int i=start; i<end; i++) {
            if (nums[i] < pv) {
                swap(nums[i], nums[div]);
                div++;
            }
        }
        swap(nums[div], nums[end]);
        return div;
    }
};