Implement the following operations of a queue using stacks.
- You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is 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).
Valid operations:
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.
Python Solution:
class MyQueue(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.ins = []
self.outs = []
def push(self, x):
"""
Push element x to the back of queue.
:type x: int
:rtype: void
"""
self.ins.append(x)
def pop(self):
"""
Removes the element from in front of queue and returns that element.
:rtype: int
"""
if not self.outs:
self.outs = self.ins[::-1]
self.ins = []
return self.outs.pop()
def peek(self):
"""
Get the front element.
:rtype: int
"""
if not self.outs:
self.outs = self.ins[::-1]
self.ins = []
return self.outs[-1]
def empty(self):
"""
Returns whether the queue is empty.
:rtype: bool
"""
return not self.ins and not self.outs
# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()
Summary:
- Two stack, one for input, the other for output.
LeetCode: 232. Implement Queue using Stacks
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