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import { ListNode } from "../mod.ts";
export default function addTwoNumbers(    l1: ListNode | null,    l2: ListNode | null,): ListNode | null {    if (!l1) {        return l2;    }    if (!l2) {        return l1;    }    const node_to_prev = new WeakMap<ListNode, ListNode | null>();
    while (l1 && l1.next) {        node_to_prev.set(l1.next, l1);        l1 = l1.next;    }    // l1 = l1.next;    while (l2 && l2.next) {        node_to_prev.set(l2.next, l2);        l2 = l2.next;    }    // l2 = l2.next;    // console.log(l1,l2)    let head = null;    // let temp: ListNode | null = head;    let p1: ListNode | null | undefined = l1;    let p2: ListNode | null | undefined = l2;    let carry = 0;    while (p1 || p2 || carry) {        if (p1) {            carry += p1.val;            p1 = node_to_prev.get(p1);        }        if (p2) {            carry += p2.val;            p2 = node_to_prev.get(p2);        }        // temp.next = new ListNode(carry % 10);        head = new ListNode(carry % 10, head);        carry = Math.floor(carry / 10);    }    return head;}