from collections import deque

def farthest_reachable(A, L):
    if A != sorted(A):
        raise ValueError("A is not sorted")
    if L <= 0:
        raise ValueError("L is not positive")

    n = len(A)

    Q = deque([A[0]])          # a double-ended queue containing A[0]
    B = []
    i = 1
    while i < n or len(Q) > 0:
        print("{0:2d}".format(i), B, list(Q))
        if i < n and (len(Q) == 0 or A[i] <= Q[0] + L):
            Q.append(A[i])     # add A[i] to the right of the deque
            i = i + 1
        else:
            B.append(Q[-1])    # append to B the rightmost elt in Q
            Q.popleft()        # remove the leftmost elt from Q
    print("{0:2d}".format(i), B, list(Q))
    return B

if __name__ == "__main__":
    print("Result:", farthest_reachable([1.0, 1.5, 2.1, 2.6, 2.9, 3.0, 4.2, 5.0, 5.2, 6.3, 7.0, 8.0, 8.5, 9.1, 9.6, 9.9, 10.0], 0.1))
    print("Result:", farthest_reachable([1.0, 1.5, 2.1, 2.6, 2.9, 3.0, 4.2, 5.0, 5.2, 6.3, 7.0, 8.0, 8.5, 9.1, 9.6, 9.9, 10.0], 3))