206. Reverse Linked List

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head==null) return head;
        ListNode pre=null;
        ListNode cur=head;
        ListNode nt=head.next;
        while(cur.next!=null)
        {
            nt=cur.next;
            cur.next=pre;
            pre=cur;
            cur=nt;
        }
        cur.next=pre;
        head=cur;
        return head;
    }
}

Javascript

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {
    if(head===null) return head;
        var pre=null;
        var cur=head;
        var nt=head.next;
        while(cur.next!==null)
        {
            nt=cur.next;
            cur.next=pre;
            pre=cur;
            cur=nt;
        }
        cur.next=pre;
        head=cur;
        return head;
};

优解，差不多

注意头节点的指针要指向空