《劍指offer》(JAVA版)——從尾到頭打印鏈表

一、題目描述

輸入一個鏈表，按鏈表從尾到頭的順序返回一個ArrayList。

輸入 ：一個鏈表的頭結點
輸出 ：按鏈表從尾到頭存儲的ArrayList

牛客NOWCODER

二、思路分析

1、使用棧。遍歷鏈表的時候，把每一個遍歷的結點放入一個棧中，遍歷完成後再從棧頂將結點輸出
2、使用遞歸的方法。

三、實現代碼

import java.util.ArrayList;
import java.util.Stack;

/**
 * @AUTHOR:0416
 * @DESCRIPTION:
 * @DATE:2019/10/17
 **/
public class PrintLinkReversely {

    static class ListNode {
        private int val;
        private ListNode next = null;
        public ListNode(int val){
            this.val = val;
        }

        public int getVal() {
            return val;
        }

        public ListNode getNext() {
            return next;
        }

        public void setNext(ListNode next) {
            this.next = next;
        }
    }

    /**
     * print the link reversely by stack class
     * @param listNode
     */
    public static ArrayList<Integer> printReverselyByStack(ListNode listNode){
        Stack stack = new Stack();
        while(listNode != null){
            stack.push(listNode.getVal());
            listNode = listNode.getNext();
        }
        ArrayList<Integer> arrayList = new ArrayList<>();
        while(!stack.isEmpty()){
            arrayList.add((Integer)stack.pop());
        }
        return arrayList;
    }

    /**
     * print the link reversely by recursion
     * @param listNode
     */
    public static ArrayList<Integer> printReverselyByRecursion(ListNode listNode){
        ArrayList<Integer> arrayList = new ArrayList<>();
        if(listNode != null){
            ArrayList temp = printReverselyByRecursion(listNode.getNext());
            arrayList.addAll(temp);
            arrayList.add(listNode.getVal());
        }
        return arrayList;
    }

    public static void main(String[] args){
        ListNode a = new ListNode(1);
        ListNode b = new ListNode(2);
        ListNode c = new ListNode(3);
        ListNode d = new ListNode(4);
        ListNode e = new ListNode(5);
        ListNode f = new ListNode(6);
        ListNode g = new ListNode(7);
        ListNode h = new ListNode(8);
        ListNode i = new ListNode(9);
        ListNode j = new ListNode(10);
        a.setNext(b);
        b.setNext(c);
        c.setNext(d);
        d.setNext(e);
        e.setNext(f);
        f.setNext(g);
        g.setNext(h);
        h.setNext(i);
        i.setNext(j);
        ArrayList arrayList = printReverselyByStack(a);
        System.out.println(arrayList.toString());
        ArrayList arrayList12 = printReverselyByRecursion(a);
        System.out.println(arrayList12.toString());
    }
}

注意：在使用 nowcoder 進行代碼測試的時候需要進行一定的修改。（例如， listNode.getVal() -> list