题解 | #反转链表#

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param pHead ListNode类
 * @return ListNode类
 */
function ReverseList(pHead) {
    // write code here
    // 判断链表为空或长度为1的情况
    if (pHead == null || pHead.next == null) {
        return pHead;
    }
    let p1 = null,
        p2 = null;
    while (pHead != null) {
        // p1: 2->3->null
        p1 = pHead.next;
        // pHead: 1->null
        pHead.next = p2;
        // p2: 1->null
        p2 = pHead;
        // pHead: 2->3->null
        pHead = p1;
    }
    return p2;
}
module.exports = {
    ReverseList: ReverseList,
};