class Node {    
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}
class SLList {
    constructor() {
        this.head = null;
        this.tail = null;
        this.size = 0;
    }
    pushLeft(data) {
        const node = new Node(data);
        node.next = this.head;
        this.head = node;
        if (this.size === 0) {
            this.tail = node;
        }
        this.size++;
    }
    pushRight(data) {
        if (this.size === 0) {
            this.pushLeft(data);
            return;
        }
        const node = new Node(data);
        this.tail.next = node;
        this.tail = node;
        this.size++;
    }
    popLeft() {
        if (this.size === 0) {
            return;
        }
        const data = this.head.data;
        this.head = this.head.next;
        this.size--;
        if (this.size === 0) {
            this.tail = null;
        }
        return data;
    }
    popRight() {
        if (this.size === 0) {
            return;
        }
        if (this.size === 1) {
            return this.popLeft();            
        }
        let node = this.head;
        while (node.next.next !== null) {
            node = node.next;
        }
        const data = this.tail.data;
        this.tail = node;
        node.next = null;
        this.size--;
    }
    reverse() {
        if (this.size < 2) {
            return;
        }
        let curr = this.head;
        let prev = null;
        let next = null;
        while (curr !== null) {
            next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        this.head = prev;
    }
    print() {
        let output = "[ ";
        let node = this.head;
        while (node) {
            output += node.data + " -> ";
            node = node.next;
        }
        output += "null ]"
        console.log(output);
    }
}

const list = new SLList();
list.popLeft();
list.popRight();
list.pushLeft(2);
list.pushLeft(1);
list.pushRight(3);
list.pushRight(4);
list.pushRight(5);
list.print();
list.reverse();
list.print();
list.popLeft();
list.popLeft();
list.popRight();
list.popRight();
list.popRight();
console.log(list);