剑指 Offer 06. 从尾到头打印链表

题解

迭代

先求出链表的长度，最后反着添加元素即可

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public int[] reversePrint(ListNode head) {
        ListNode node = head;
        int count = 0;
        while(node != null){
            node = node.next;
            count ++;
        }
        int[] res = new int[count];
        for(int i = count - 1; i >= 0; -- i){
            res[i] = head.val;
            head = head.next;
        }

        return res;
    }
}

回溯

直接利用回溯算法直接就是从后面添加

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    List<Integer> list = new ArrayList<>();
    public int[] reversePrint(ListNode head) {
        backTracking(head);
        int[] res = new int[list.size()];
        for(int i = 0; i < list.size(); ++ i){
            res[i] = list.get(i);
        }
        return res;
    }

    void backTracking(ListNode head){
        if(head == null) return;
        backTracking(head.next);
        list.add(head.val);
    }
}