206. Reverse Linked List #

题目 #

给定单链表头节点head，反转并返回反转后的链表。

思路 #

代码 #

递归 #

public class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}
class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }
}

迭代 #

public class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null, cur = head, next = head.next;
        while (cur != null) {
            cur.next = prev;
            prev = cur;
            cur = next;
            if (next != null) next = next.next;
        }
        return prev;
    }
}