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232.ImplementQueueusingStacks.py
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232.ImplementQueueusingStacks.py
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"""
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.
Example:
MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
queue.peek(); // returns 1
queue.pop(); // returns 1
queue.empty(); // returns false
Notes:
- 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).
"""
#Difficulty: Easy
#17 / 17 test cases passed.
#Runtime: 44 ms
#Memory Usage: 13.7 MB
#Runtime: 44 ms, faster than 18.18% of Python3 online submissions for Implement Queue using Stacks.
#Memory Usage: 13.7 MB, less than 94.52% of Python3 online submissions for Implement Queue using Stacks.
class MyQueue:
def __init__(self):
"""
Initialize your data structure here.
"""
self.stack = []
def push(self, x: int) -> None:
"""
Push element x to the back of queue.
"""
self.stack.append(x)
self.stack.insert(0, self.stack.pop())
def pop(self) -> int:
"""
Removes the element from in front of queue and returns that element.
"""
if self.stack:
return self.stack.pop()
def peek(self) -> int:
"""
Get the front element.
"""
if self.stack:
return self.stack[-1]
def empty(self) -> bool:
"""
Returns whether the queue is empty.
"""
return not self.stack
# 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()