Q = [None]*100   # fixed-size array to store the elements in the queue

Front = 0        # points to the element that is in front of the queue

Back = 0         # points to the first element past the last in the
                 # queue, which is where you would enqueue the next
                 # element

def next(p):
    global Q
    p = p + 1
    if p == len(Q):
        p = 0
    return p

def is_empty():
    global Front, Back
    return Front == Back

def is_full():
    global Front, Back
    return next(Back) == Front

def enqueue(x):
    global Q, Front, Back
    if is_full():
        print('queue full')
    else:
        Q[Back] = x
        Back = next(Back)

def dequeue():
    global Q, Front, Back
    if is_empty():
        print('queue empty')
    else:
        x = Q[Front]
        Front = next(Front)
        return x