JZ-015-Reverse linked list

Reverse linked list

Title description

Input a linked list, after inverting the linked list, output the header of the new linked list.

title link : reverse linked list

Code

/**
 * 标题：反转链表
 * 题目描述
 * 输入一个链表，反转链表后，输出新链表的表头。
 * 题目链接：
 * https://www.nowcoder.com/practice/75e878df47f24fdc9dc3e400ec6058ca?tpId=13&&tqId=11168&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking
 */
public class Jz15 {

    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode first = head, second = head.next;
        first.next = null;
        while (first != null && second != null) {
            ListNode temp = first;
            first = second;
            second = second.next;
            first.next = temp;
        }
        return first;
    }

    public static void main(String[] args) {
        ListNode head = new ListNode(1);
        head.next = new ListNode(2);
        head.next.next = new ListNode(3);
        System.out.println("before reverse");
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
        Jz15 jz15 = new Jz15();
        ListNode result = jz15.reverseList(head);
        System.out.println("after reverse");
        ListNode cur1 = result;
        while (cur1 != null) {
            System.out.print(cur1.val + " ");
            cur1 = cur1.next;
        }
    }
}

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