const debug = require('debug')('reverseLinkedList');

class ListNode {

constructor(val) {

this.val = val;

this.next = null;

}

}

// create a list: 1 -> 2 -> 3 -> 4 -> 5 -> null

const headNode = new ListNode(1);

let currentNode = headNode;

for (let i = 2; i <= 5; i += 1) {

currentNode.next = new ListNode(i);

currentNode = currentNode.next;

}

// Iterative Approach -> O(n), O(1)

const iterativeReverse = (head) => {

let pre = null;

let cur = head;

while (cur) {

const tmp = cur.next;

cur.next = pre;

pre = cur;

cur = tmp;

}

return pre;

};

const h1 = iterativeReverse(headNode);

debug(h1);

// Recursive Appoach -> O(n), O(n)

const recursiveReverse = (head) => {

const curNode = head;

if (curNode === null || curNode.next === null) {

return curNode;

}

const p = recursiveReverse(curNode.next);

curNode.next.next = curNode;

curNode.next = null;

return p;

};

const h2 = recursiveReverse(headNode);

debug(h2);