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queue-two-stacks.py
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queue-two-stacks.py
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from stack import ArrayStack, StackOverflowError, StackUnderflowError
class TwoStackQueue():
def __init__(self, length):
self.stack_first = ArrayStack(length)
self.stack_second = ArrayStack(length)
def enqueue(self, value):
self.stack_first.push(value)
def dequeue(self):
while self.stack_first.top != 0:
self.stack_second.push(self.stack_first.pop())
value = self.stack_second.pop()
while self.stack_second.top != 0:
self.stack_first.push(self.stack_second.pop())
return value
two_stack_queue = TwoStackQueue(7)
two_stack_queue.enqueue(1)
two_stack_queue.enqueue(2)
two_stack_queue.enqueue(3)
two_stack_queue.enqueue(4)
two_stack_queue.enqueue(5)
two_stack_queue.enqueue(6)
two_stack_queue.enqueue(7)
try:
two_stack_queue.enqueue(8)
raise Exception("We can't go there, stack overderflow must be raised")
except StackOverflowError:
pass
assert two_stack_queue.dequeue() == 1
assert two_stack_queue.dequeue() == 2
assert two_stack_queue.dequeue() == 3
assert two_stack_queue.dequeue() == 4
assert two_stack_queue.dequeue() == 5
assert two_stack_queue.dequeue() == 6
assert two_stack_queue.dequeue() == 7
try:
two_stack_queue.dequeue()
raise Exception("We can't go there, stack underderflow must be raised")
except StackUnderflowError:
pass
two_stack_queue.enqueue(1)
two_stack_queue.enqueue(2)
two_stack_queue.enqueue(3)
two_stack_queue.enqueue(4)
two_stack_queue.enqueue(5)
two_stack_queue.enqueue(6)
two_stack_queue.enqueue(7)
assert two_stack_queue.dequeue() == 1
assert two_stack_queue.dequeue() == 2
two_stack_queue.enqueue(6)
two_stack_queue.enqueue(7)
assert two_stack_queue.dequeue() == 3
assert two_stack_queue.dequeue() == 4