206. Reverse Linked List - jiejackyzhang/leetcode-note GitHub Wiki

Reverse a singly linked list.

Linked List类题目

##Approach 1: Iterative

/**
 * 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) {
        ListNode pre = null;
        ListNode cur = head;
        while(cur != null) {
            ListNode post = cur.next;
            cur.next = pre;
            pre = cur;
            cur = post;
        }
        return pre;
    }
}

##Approach 2: Recursive 递归需要注意的一点是需要把head.next指向null，否则第一个节点和第二个节点之间会存在环。

/**
 * 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 || head.next == null) {
            return head;
        }
        ListNode p = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return p;
    }
}