Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty). Implement the MyQueue class:
- void push(int x) Pushes element x to the back of the queue.
- int pop() Removes the element from the front of the queue and returns it.
- int peek() Returns the element at the front of the queue.
- boolean empty() Returns true if the queue is empty, false otherwise.
pop and peek are valid.Input
["MyQueue", "push", "push", "peek", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 1, 1, false]
Explanation
MyQueue myQueue = new MyQueue();
myQueue.push(1); // queue is: [1]
myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
myQueue.peek(); // return 1
myQueue.pop(); // return 1, queue is [2]
myQueue.empty(); // return false
class MyQueue:
def __init__(self):
"""
Initialize your data structure here.
"""
self.stack = []
self._lenth = 0
def push(self, x: int) -> None:
"""
Push element x to the back of queue.
"""
self.stack.append(x)
self._lenth += 1
def pop(self) -> int:
"""
Removes the element from in front of queue and returns that element.
"""
if self.empty():
return None
self._lenth -= 1
return self.stack.pop(0)
def peek(self) -> int:
"""
Get the front element.
"""
if self.empty():
return None
return self.stack[0]
def empty(self) -> bool:
"""
Returns whether the queue is empty.
"""
return self._lenth == 0
Runtime: 32 ms, faster than 55.71% of Python3 online submissions for Implement Queue using Stacks. Memory Usage: 14.5 MB, less than 12.11% of Python3 online submissions for Implement Queue using Stacks.