Diffk

• Time : $O(n)$
• Space : $O(1)$

int Solution::diffPossible(vector<int> &A, int B) {
    int l = 0, r = 1, n = A.size();
    B = abs(B);
    while(r < n) {
        while(r < n and A[l] + B > A[r]) r++;
        if(l == r) r++;
        if(r >= n) return false;
        if(A[l] + B == A[r] and l != r) return true;
        while(l < r and A[l] + B < A[r]) l++;
    }
    return false;
}