Stack

class Stack {
    constructor() {
        this.items = [];
        this.top = null;
    }
    getTop() {
        return this.isEmpty() ? null : this.top;
    }
    isEmpty() {
        return this.items.length === 0;
    }
    size() {
        return this.items.length;
    }
    push(element) {
        this.items.push(element);
        this.top = element;
    }
    pop() {
        if (this.items.length === 0) {
            return null;
        }
        if (this.items.length === 1) {
            this.top = null;
            return this.items.pop();
        }
        this.top = this.items[this.items.length - 2];
        return this.items.pop();
    }
}

const stack = new Stack();

Operation	Time Complexity
isEmpty	O(1)
getTop	O(1)
size	O(1)
push	O(1)
pop	O(1)

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