This content originally appeared on DEV Community and was authored by Abhishek Chaudhary
Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).
Implement the MyStack class:
-
void push(int x)Pushes element x to the top of the stack. -
int pop()Removes the element on the top of the stack and returns it. -
int top()Returns the element on the top of the stack. -
boolean empty()Returnstrueif the stack is empty,falseotherwise.
Notes:
- You must use only standard operations of a queue, which means that only
push to back,peek/pop from front,sizeandis emptyoperations are valid. - Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations.
Example 1:
Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 2, 2, false]
Explanation
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False
Constraints:
-
1 <= x <= 9 - At most
100calls will be made topush,pop,top, andempty. - All the calls to
popandtopare valid.
Follow-up: Can you implement the stack using only one queue?
SOLUTION:
class MyStack:
def __init__(self):
self.stack = []
def push(self, x: int) -> None:
self.stack.append(x)
def pop(self) -> int:
if not self.empty():
return self.stack.pop()
def top(self) -> int:
if not self.empty():
return self.stack[-1]
def empty(self) -> bool:
return len(self.stack) == 0
# Your MyStack object will be instantiated and called as such:
# obj = MyStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()
This content originally appeared on DEV Community and was authored by Abhishek Chaudhary
Abhishek Chaudhary | Sciencx (2022-06-16T14:30:37+00:00) Implement Stack using Queues. Retrieved from https://www.scien.cx/2022/06/16/implement-stack-using-queues/
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