LeetCode/ReverseLinkedList.java at master · Orio77/LeetCode · GitHub

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/**
 * Definition for singly-linked list.
 * 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; }
 * }
 */
/**
 * ReverseLinkedList
 */

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null) {
            return null;
        }
        if (head.next == null) {
            return head;
        }

        ListNode nextNode = head.next;
        head.next = null;

        while (nextNode != null) {
            ListNode nextNextNode = nextNode.next;

            nextNode.next = head;
            head = nextNode;
            nextNode = nextNextNode;
        }
        return head;
    }
}

class ListNode {
    int val;
    ListNode next;
    ListNode() {

    }
    ListNode(int val) {
        this.val = val;
    }
    ListNode(int val, ListNode next) {
        this.val = val; this.next = next;
    }
}