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Queue implementation using two Stacks (#8617)
* Queue implementation using two Stacks * fix typo in queue/queue_on_two_stacks.py * add 'iterable' to queue_on_two_stacks initializer * make queue_on_two_stacks.py generic class * fix ruff-UP007 in queue_on_two_stacks.py * enhance readability in queue_on_two_stacks.py * Create queue_by_two_stacks.py --------- Co-authored-by: Christian Clauss <cclauss@me.com>
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amirsoroush
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115
data_structures/queue/queue_by_two_stacks.py
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115
data_structures/queue/queue_by_two_stacks.py
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"""Queue implementation using two stacks"""
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from collections.abc import Iterable
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from typing import Generic, TypeVar
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_T = TypeVar("_T")
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class QueueByTwoStacks(Generic[_T]):
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def __init__(self, iterable: Iterable[_T] | None = None) -> None:
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"""
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>>> QueueByTwoStacks()
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Queue(())
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>>> QueueByTwoStacks([10, 20, 30])
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Queue((10, 20, 30))
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>>> QueueByTwoStacks((i**2 for i in range(1, 4)))
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Queue((1, 4, 9))
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"""
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self._stack1: list[_T] = list(iterable or [])
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self._stack2: list[_T] = []
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def __len__(self) -> int:
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"""
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>>> len(QueueByTwoStacks())
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0
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>>> from string import ascii_lowercase
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>>> len(QueueByTwoStacks(ascii_lowercase))
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26
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>>> queue = QueueByTwoStacks()
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>>> for i in range(1, 11):
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... queue.put(i)
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...
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>>> len(queue)
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10
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>>> for i in range(2):
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... queue.get()
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1
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2
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>>> len(queue)
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8
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"""
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return len(self._stack1) + len(self._stack2)
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def __repr__(self) -> str:
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"""
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>>> queue = QueueByTwoStacks()
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>>> queue
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Queue(())
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>>> str(queue)
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'Queue(())'
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>>> queue.put(10)
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>>> queue
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Queue((10,))
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>>> queue.put(20)
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>>> queue.put(30)
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>>> queue
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Queue((10, 20, 30))
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"""
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return f"Queue({tuple(self._stack2[::-1] + self._stack1)})"
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def put(self, item: _T) -> None:
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"""
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Put `item` into the Queue
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>>> queue = QueueByTwoStacks()
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>>> queue.put(10)
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>>> queue.put(20)
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>>> len(queue)
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2
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>>> queue
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Queue((10, 20))
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"""
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self._stack1.append(item)
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def get(self) -> _T:
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"""
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Get `item` from the Queue
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>>> queue = QueueByTwoStacks((10, 20, 30))
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>>> queue.get()
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10
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>>> queue.put(40)
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>>> queue.get()
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20
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>>> queue.get()
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30
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>>> len(queue)
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1
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>>> queue.get()
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40
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>>> queue.get()
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Traceback (most recent call last):
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...
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IndexError: Queue is empty
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"""
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# To reduce number of attribute look-ups in `while` loop.
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stack1_pop = self._stack1.pop
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stack2_append = self._stack2.append
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if not self._stack2:
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while self._stack1:
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stack2_append(stack1_pop())
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if not self._stack2:
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raise IndexError("Queue is empty")
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return self._stack2.pop()
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if __name__ == "__main__":
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from doctest import testmod
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testmod()
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137
data_structures/queue/queue_on_two_stacks.py
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137
data_structures/queue/queue_on_two_stacks.py
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"""Queue implementation using two stacks"""
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from collections.abc import Iterable
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from typing import Generic, TypeVar
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_T = TypeVar("_T")
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class QueueByTwoStacks(Generic[_T]):
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def __init__(self, iterable: Iterable[_T] | None = None) -> None:
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"""
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>>> queue1 = QueueByTwoStacks()
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>>> str(queue1)
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'Queue([])'
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>>> queue2 = QueueByTwoStacks([10, 20, 30])
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>>> str(queue2)
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'Queue([10, 20, 30])'
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>>> queue3 = QueueByTwoStacks((i**2 for i in range(1, 4)))
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>>> str(queue3)
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'Queue([1, 4, 9])'
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"""
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self._stack1: list[_T] = [] if iterable is None else list(iterable)
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self._stack2: list[_T] = []
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def __len__(self) -> int:
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"""
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>>> queue = QueueByTwoStacks()
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>>> for i in range(1, 11):
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... queue.put(i)
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...
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>>> len(queue) == 10
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True
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>>> for i in range(2):
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... queue.get()
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1
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2
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>>> len(queue) == 8
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True
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"""
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return len(self._stack1) + len(self._stack2)
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def __repr__(self) -> str:
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"""
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>>> queue = QueueByTwoStacks()
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>>> queue
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Queue([])
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>>> str(queue)
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'Queue([])'
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>>> queue.put(10)
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>>> queue
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Queue([10])
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>>> queue.put(20)
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>>> queue.put(30)
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>>> queue
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Queue([10, 20, 30])
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"""
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items = self._stack2[::-1] + self._stack1
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return f"Queue({items})"
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def put(self, item: _T) -> None:
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"""
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Put `item` into the Queue
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>>> queue = QueueByTwoStacks()
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>>> queue.put(10)
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>>> queue.put(20)
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>>> len(queue) == 2
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True
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>>> str(queue)
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'Queue([10, 20])'
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"""
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self._stack1.append(item)
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def get(self) -> _T:
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"""
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Get `item` from the Queue
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>>> queue = QueueByTwoStacks()
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>>> for i in (10, 20, 30):
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... queue.put(i)
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>>> queue.get()
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10
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>>> queue.put(40)
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>>> queue.get()
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20
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>>> queue.get()
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30
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>>> len(queue) == 1
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True
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>>> queue.get()
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40
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>>> queue.get()
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Traceback (most recent call last):
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...
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IndexError: Queue is empty
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"""
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# To reduce number of attribute look-ups in `while` loop.
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stack1_pop = self._stack1.pop
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stack2_append = self._stack2.append
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if not self._stack2:
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while self._stack1:
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stack2_append(stack1_pop())
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if not self._stack2:
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raise IndexError("Queue is empty")
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return self._stack2.pop()
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def size(self) -> int:
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"""
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Returns the length of the Queue
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>>> queue = QueueByTwoStacks()
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>>> queue.size()
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0
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>>> queue.put(10)
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>>> queue.put(20)
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>>> queue.size()
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2
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>>> queue.get()
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10
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>>> queue.size() == 1
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True
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"""
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return len(self)
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if __name__ == "__main__":
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from doctest import testmod
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testmod()
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