【剑指 Offer 06. 从尾到头打印链表】

淩亂°似流年 2023-09-26 16:43 74阅读 0赞

package com.example.demomain.demoleetcode.easy;
    
    import com.example.demomain.demoleetcode.medium.ListNode;
    import org.junit.Test;
    
    import java.util.Arrays;
    
    /**
     * 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）。
     * <p>
     * 示例 1：
     * <p>
     * 输入：head = [1,3,2]
     * 输出：[2,3,1]
     * 限制：
     * <p>
     * 0 <= 链表长度 <= 10000
     *
     * @author: lfsun
     * @time: 17:02
     * @date: 2022/11/16
     */
    public class ReversePrint {
        
        public int[] reversePrint(ListNode head) {
        
            if (head == null) {
        
                return new int[]{
        };
            }
            // 构造初始数组
            int[] ints = new int[10000];
            // 索引 统计个数
            int index = 0;
            while (head != null) {
        
                ints[index++] = head.val;
                ListNode temp = head.next;
                head.next = head;
                head = temp;
            }
            // 只要有数据的那部分数组
            int[] res = Arrays.copyOf(ints, index);
            // 翻转数组
            for (int i = 0; i < res.length / 2; i++) {
        
                int temp = res[i];
                res[i] = res[res.length - 1 - i];
                res[res.length - 1 - i] = temp;
            }
            return res;
        }
    
        @Test
        public void test() {
        
            ListNode head = new ListNode(1);
            ListNode head1 = new ListNode(2);
            ListNode head2 = new ListNode(3);
            ListNode head3 = new ListNode(4);
            ListNode head4 = new ListNode(5);
            head.next = head1;
            head1.next = head2;
            head2.next = head3;
            head3.next = head4;
            System.out.println(Arrays.toString(reversePrint(head)));
    
        }
    }