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import { Node } from "./Node.ts";
const head_to_end = new WeakMap<Node, Node>();function flatten(head: Node | null): Node | null {    if (!head) {        return null;    }
    let p: Node | null | undefined = head;    let last: Node | null | undefined = null;    while (p) {        last = p;        if (p.child) {            const next = p.next;            const child = flatten(p.child);            p.next = child;            if (child) {                child.prev = p;            }            p.child = null;
            // let end = child;            // while (end && end.next) {            //     end = end.next;            // }            const end = child && head_to_end.get(child);            if (end && next) {                end.next = next;                next.prev = end;            }        }        p = p.next;    }    last && head_to_end.set(head, last);    //  console.log(head)    return head;}export default flatten;