658

class Solution {
public:
    vector<int> findClosestElements(vector<int>& arr, int k, int x) {
        int left=0, right=arr.size()-k;

        // Binary search the first val in range [0, n-k].
        // Decide where to move the sliding window based on 4 conditions.
        // Here leftmost bs is used since we want the leftmost starting point satisfying all conditions.
        while(left<right){
            int mid = (left+right)/2;
            if(x-arr[mid] > arr[mid+k]-x)
                left = mid+1;
            else
                right = mid;
        }

        // Get the elements of sliding window in vector and return.
        vector<int> ans;
        for(int i=left; i<left+k; i++)
            ans.push_back(arr[i]);
        return ans;
    }
};