Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (
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.
trueif the queue is empty,
- You must use only standard operations of a stack, which means only
push to top,
peek/pop from top,
is emptyoperations are valid.
- Depending on your language, the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations.
Follow-up: Can you implement the queue such that each operation is amortized
O(1) time complexity? In other words, performing
n operations will take overall
O(n) time even if one of those operations may take longer.
Input ["MyQueue", "push", "push", "peek", "pop", "empty"] [, , , , , ] Output [null, null, null, 1, 1, false] Explanation MyQueue myQueue = new MyQueue(); myQueue.push(1); // queue is:  myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue) myQueue.peek(); // return 1 myQueue.pop(); // return 1, queue is  myQueue.empty(); // return false
1 <= x <= 9
- At most
100calls will be made to
- All the calls to
Solution in python
class MyQueue: def __init__(self): self.queue = deque() def push(self, x: int) -> None: self.queue.append(x) def pop(self) -> int: return self.queue.popleft() def peek(self) -> int: return self.queue def empty(self) -> bool: return False if self.queue else True # 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()