leetcode206-反转链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        ListNode* preNode = nullptr;
        ListNode* curNode = head;
        while(curNode && curNode->next){
            ListNode* tmp = curNode->next;
            curNode->next = preNode;
            preNode = curNode;
            curNode = tmp;
        }
        if(curNode){ //此处一开始没注意可能为空数组的情况。
            curNode->next = preNode;        
        }
        return curNode;
    }
};

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */

var reverseList = function(head) {
    let preNode = null;
    let curNode = head;
    while(curNode){
        let temp = curNode.next;
        curNode.next = preNode;
        preNode = curNode;
        curNode = temp;
    }
    return preNode;
};