算法-6.从尾到头打印链表

从尾到头打印链表

输入一个链表的头节点，从尾到头反过来返回每个节点的值（用数组返回）
思路：首先需要对链表进行逆序
然后再对将链表保存在数组中

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
    public int[] reversePrint(ListNode head) {
        ListNode pre = null;    
        ListNode cur = head;
        ListNode next = null;

        while (cur != null) {
            next = cur.next;

            cur.next = pre;
            pre = cur;
            cur = next;

        }

        ListNode reverseListNode = pre;
        ArrayList<Integer> list = new ArrayList<>();
        while (reverseListNode != null) {
            list.add(reverseListNode.val);
            reverseListNode = reverseListNode.next;
        }
        int[] array = new int[list.size()];
        for(int i=0;i<list.size();i++) {
            array[i] = list.get(i);
        }
        return array;
    }

附：链表反转

    public static ListNode reverse(ListNode head) {
        ListNode pre = head;
        ListNode cur = head.next;
        ListNode next = null;

        head.next = null;
        while (cur != null) {
            next = cur.next;
            cur.next = pre;
            pre = cur;
            cur = next;
        }
        return pre;
    }

    public static ListNode reverse1(ListNode head) {
        ListNode pre = null;
        ListNode cur = head;
        ListNode next = null;

        // next = 2
        // pre = 0
        // cur = 1
        while (cur != null) {
            next = cur.next;

            cur.next = pre;
            pre = cur;
            cur = next;

        }
        return pre;
    }