Design Stack (Array-backed)

Problem

Design a class MyStack using an array. Implement push(int), pop() (returns the popped value), top(), and empty().

Constraints

• 1 ≤ ops ≤ 1000

Approach — Stack

This is a Stack problem. The idea: scan the input once, pushing work onto a stack and popping when the top can be resolved, so the stack always reflects what's still open. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(n) space.

Solution code

Python

class MyStack:
    def __init__(self):
        self.data = []

    def push(self, x):
        self.data.append(x)

    def pop(self):
        return self.data.pop()

    def top(self):
        return self.data[-1]

    def empty(self):
        return len(self.data) == 0

Java

class MyStack {
    private int[] buf = new int[10000];
    private int n = 0;
    public void push(int x) { buf[n++] = x; }
    public int pop() { return buf[--n]; }
    public int top() { return buf[n - 1]; }
    public boolean empty() { return n == 0; }
}

class Solution {}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.