K_CLOSEST_ELEMENTS

class Solution {
public:
    //f(i) = abs(a[i] - x)
    // g(i) = f(i) <= f(i+k)
    // 00 111111
    //TC: O(log(n-k))
    vector<int> findClosestElements(vector<int>& arr, int k, int x) {
        int n = arr.size();

        int lo = 0;
        int hi = n - k;
        int mid;
        while(lo < hi)
        {
            mid = lo + (hi - lo)/2;

            if(x - arr[mid]  > arr[mid+k] - x)
            {
                lo = mid + 1;
            }
            else
            {
                hi = mid;
            }
        }

        return vector<int>(arr.begin() + lo, arr.begin() + lo + k);
    }
};