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Implement Queue using Stacks
Implement the following operations of a queue using stacks.
- push(x) -- Push element x to the back of queue.
- pop() -- Removes the element from in front of queue.
- peek() -- Get the front element.
- empty() -- Return whether the queue is empty.
- You must use only standard operations of a stack -- which means only
push to top
,peek/pop from top
,size
, andis empty
operations are valid. - Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
- You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).
分析:
用栈实现队列,需要两个栈来回传输元素。
代码:
class Queue(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.st1 = []
self.st2 = []
def push(self, x):
"""
:type x: int
:rtype: nothing
"""
self.move(self.st1, self.st2)
self.st1.append(x)
def pop(self):
"""
:rtype: nothing
"""
self.move(self.st2, self.st1)
self.st2.pop()
def peek(self):
"""
:rtype: int
"""
self.move(self.st2, self.st1)
return self.st2[-1]
def empty(self):
"""
:rtype: bool
"""
if self.st1 or self.st2:
return False
return True
def move(self, st1, st2):
"""
:Move st2 to st1
"""
while st2:
st1.append(st2.pop())
本文标签: implementLeetCodeStacksQueue
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