题解 | #反转链表#

1. 思路分析

创建链表是将节点依次插入到链表尾部，而反转链表的话，只需要将节点取出来放到头部。为了方便可以做一个哨兵节点$dummydummy$，每次将节点插入到$dummydummy$后即可，最后返回$dummy\mathrm{.}nextdummy.next$。

2. 代码实现

function ListNode(x){
    this.val = x;
    this.next = null;
}
function ReverseList(head) {
    if(!head || !head.next) return head;
    const dummy = new ListNode();
    let cur = head;
    while(cur) {
        if(cur == head) {
            dummy.next = new ListNode(cur.val);
        }else {
            let node = new ListNode(cur.val);
            node.next = dummy.next;
            dummy.next = node;
        }
        cur = cur.next
    }
    return dummy.next;
}
module.exports = {
  ReverseList: ReverseList,
};