Leetcode Minimum Moves to Equal Array Elements II problem solution

count = 0
    nums.sort()
    middle_element = nums[len(nums)//2]        
    for num in nums:
        count += abs(middle_element - num)     
    return count

public class Solution {
    public int minMoves2(int[] nums) {
        if (nums == null) return 0;
        
        Arrays.sort(nums);
        int k = (nums.length + 1) >> 1;
        int sum = 0;
        
        for (int i = 0; i< (nums.length >> 1); i++) {
            sum += nums[k+i] - nums[i];
        }
        return sum;      
    }
}

class Solution {
public:    
    int partition(vector<int> &nums, int l, int r) {
        int len = r - l + 1;
        int index = (rand() % len) + l;
        swap(nums[index], nums[r]);
        int pivot = nums[r];        
        int less = l;
        for (int i = l; i < r; i++) {
            if (nums[i] <= pivot) {
                swap(nums[i], nums[less++]);
            }
        }        
        swap(nums[less], nums[r]);        
        return less;
    }    
    int selectK(vector<int> &nums, int k, int l , int r) {
        if (l >= r) return l;        
        int pivot_index = partition(nums, l, r);        
        if (pivot_index - l + 1 == k) {
            return pivot_index;
        } else if (pivot_index - l + 1 < k) {
            return selectK(nums, k - (pivot_index - l + 1), pivot_index + 1, r);
        } else {
            return selectK(nums, k, l, pivot_index - 1);
        }
    }    
    int minMoves2(vector<int>& nums) {
        if (nums.empty()) return 0;        
        int median = nums.size() / 2;        
        int middle = nums[selectK(nums, median + 1, 0, nums.size() - 1)];
        int count = 0;
        for (int n : nums) {
            if (n > middle) {
                count += n - middle;
            } else {
                count += middle - n;
            }
        }        
        return count;
    }
};