5-51 两个有序链表序列的合并(Java)

5-51 两个有序链表序列的合并 (20分)

已知两个非降序链表序列S1与S2，设计函数构造出S1与S2的并集新非降序链表S3。
输入格式:

输入分两行，分别在每行给出由若干个正整数构成的非降序序列，用−1-1−1表示序列的结尾（−1-1−1不属于这个序列）。数字用空格间隔。
输出格式:

在一行中输出合并后新的非降序链表，数字间用空格分开，结尾不能有多余空格；若新链表为空，输出NULL。
输入样例:

1 3 5 -12 4 6 8 10 -1

输出样例:

1 2 3 4 5 6 8 10

找错误：

import java.util.*;public class PTA51 {// 要改成static class ListNode    class ListNode {        int val;        ListNode next;        ListNode(int x) {            val = x;        }    }    public static void main(String[] args) {        ListNode l1 = getListNode();        ListNode l2 = getListNode();        // merge two lists        ListNode res = mergeTwoLists(l1, l2);        System.out.println(res);    }    private static ListNode getListNode() {        Scanner in = new Scanner(System.in);        List<Integer> list = new ArrayList<>();    // 用hasNextInt()会一直等待输入，无法停止    // 而且两次用nextInt就指向两个不同的数，应该先存起来再输出    /*改成：    while (true) {            int i = in.nextInt();            if (i == -1) break;            list.add(i);        }    */        while (in.hasNextInt() && in.nextInt() > 0) {            list.add(in.nextInt());        }        int[] intList = new int[list.size()];        for (int i = 0; i < list.size(); i ++) {            intList[i] = list.get(i);        }        return buildListNode(intList);    }    private static ListNode buildListNode(int[] input) {        ListNode first = null, last = null, newNode;        if (input.length > 0) {            for (int i = 0; i < input.length && input[i] > 0; i ++) {                newNode = new ListNode(input[i]);                newNode.next = null;                if (first == null) {                    first = newNode;                    last = newNode;                } else {                    last.next = newNode;                    last = newNode;                }            }        }        return first;    }    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {        if (l1 == null) return l2;        if (l2 == null) return l1;        if (l1.val <= l2.val) {            l1.next = mergeTwoLists(l1.next, l2);        } else {            l2.next = mergeTwoLists(l2.next, l1);            return l2;        }    }}

修改完善后的代码：

import java.util.*;public class PTA51 {    static class ListNode {        int val;        ListNode next;        ListNode(int x) {            val = x;        }    }    public static void main(String[] args) {        ListNode l1 = getListNode();        ListNode l2 = getListNode();        // merge two lists        ListNode res = mergeTwoLists(l1, l2);        if (res == null) {            System.out.println("NULL");            return;        }        while (res != null) {            if (res.next == null) {                System.out.println(res.val);                break;            }            System.out.print(res.val + " ");            res = res.next;        }    }    private static ListNode getListNode() {        Scanner in = new Scanner(System.in);        List<Integer> list = new ArrayList<>();        while (true) {            int i = in.nextInt();            if (i == -1) break;            list.add(i);        }        int[] intList = new int[list.size()];        for (int i = 0; i < list.size(); i ++) {            intList[i] = list.get(i);        }        return buildListNode(intList);    }    private static ListNode buildListNode(int[] input) {        ListNode first = null, last = null, newNode;        if (input.length > 0) {            for (int i = 0; i < input.length && input[i] > 0; i ++) {                newNode = new ListNode(input[i]);                newNode.next = null;                if (first == null) {                    first = newNode;                    last = newNode;                } else {                    last.next = newNode;                    last = newNode;                }            }        }        return first;    }    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {        if (l1 == null) return l2;        if (l2 == null) return l1;        if (l1.val <= l2.val) {            l1.next = mergeTwoLists(l1.next, l2);            return l1;        } else {            l2.next = mergeTwoLists(l2.next, l1);            return l2;        }    }}

网上找的相似答案：

import java.util.Collections;import java.util.LinkedList;import java.util.List;public class SumTwoLinkedList {    public static void main(String[] args) {        List<Integer> list1 = new LinkedList<Integer>();        Collections.addAll(list1, 30, 41, 15, 12, 56, 80);        List<Integer> list2 = new LinkedList<Integer>();        Collections.addAll(list2, 23, 56, 78, 23, 12, 33, 79, 90, 55);        test1(list1, list2);    }    public static void test1(List<Integer> list1, List<Integer> list2) {        list1.removeAll(list2);// list1中删除和list2中交集的元素        list2.addAll(list1);// 合并        Collections.sort(list2);        for (Integer integer : list2) {            System.out.print(integer + " ");        }    }}