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, 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).



  • push(x),先将s中的元素全部弹出来,存入tmp,把x push 到tmp,然后把tmp中的元素全部弹出来,存入s
  • pop(),直接将s的栈顶元素弹出来即可

该算法push的算法复杂度是O(n), pop的算法复杂度O(1)

另个一个方法是,让popO(n), pushO(1),思路很类似,就不赘述了。



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