LeetCode 206. Reverse Linked List

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问题

Reverse a singly linked list.
public class Solution206 {    public static void main(String args[]){        Solution206 solution206 = new Solution206();        ListNode listNode1 = new ListNode(1);        ListNode listNode2 = new ListNode(2);        ListNode listNode3 = new ListNode(3);        ListNode listNode4 = new ListNode(4);        listNode1.next = listNode2;        listNode2.next = listNode3;        listNode3.next = listNode4;        ListNode head = solution206.reverseList(listNode1);        System.out.println(head.val);        System.out.println(head.next.val);        System.out.println(head.next.next.val);        System.out.println(head.next.next.next.val);    }    /**     * 创建一个新的链表,是倒序的     */    public ListNode reverseList(ListNode head) {        if(head==null || head.next==null){            return head;        }        int length=0;        ListNode currentNode = head;        while(true){            if(currentNode.next!=null){                currentNode = currentNode.next;                length++;            }else{                break;            }        }        ListNode newNode = new ListNode(currentNode.val);        ListNode firstNode = newNode;        for(int i=0;i<length;i++){            int value = getNodeValue(head, length-i);            newNode.next = new ListNode(value);            newNode = newNode.next;        }        return firstNode;    }    public int getNodeValue(ListNode head, int n) {        for(int i=1;i<n;i++){            head = head.next;        }        return head.val;    }//    /**//     * 解析答案//     *///    public ListNode reverseList(ListNode head) {////        ListNode pre     = null;//        ListNode current = head;//        while(current!=null){//            ListNode next_temp = current.next;//            current.next = pre;//            pre = current;//            current = next_temp;//        }//        return pre;//    }    public static class ListNode {        int val;        ListNode next;        ListNode(int x) { val = x; }    }}
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