1 package com.algorithm;
2
3 public class MergeList {
4 public ListNode Merge(ListNode list1,ListNode list2) {
5 //运行时间：32ms
6 //占用内存：688k
7 //输入两个单调递增的链表，输出两个链表合成后的链表，当然我们需要合成后的链表满足单调不减规则。
8 //第一次比较
9 if(list1 == null)
10 return list2;
11 if(list2 == null)
12 return list1;
13 ListNode listGuard = null;//哨兵，存储链表头指针
14 ListNode listroot = null;
15 //然后每次比较两条链表的每一个结点的大小，如果小的，那么将哨兵的next指向它，再
16 //将小的节点指向next
17 if(list1.val <= list2.val) {
18 listroot = list1;
19 listGuard = list1;
20 list1 = list1.next;
21 }else{
22 listroot = list2;
23 listGuard = list2;
24 list2 = list2.next;
25 }
26 while(list1 != null && list2 != null){
27 if(list1.val <= list2.val){//如果第一条链表小于第二条链表
28 listGuard.next = list1;
29 listGuard = list1;
30 list1 = list1.next;
31 }else{
32 listGuard.next = list2;
33 listGuard = list2;
34 list2 = list2.next;
35 }
36 }
37 //循环遍历完了，如果第一个不等于空，则说明后面还有数据，直接移动指针listGuard即可
38 if(list1 != null) {
39 listGuard.next = list1;42 }
43 if(list2 != null) {
44 listGuard.next = list2;47 }
48 return listroot;
49 }
50 public static void main(String[] args) {
51 ListNode la = new ListNode(1);
52 ListNode lb = new ListNode(3);
53 ListNode lc = new ListNode(9);
54 la.next = lb;
55 lb.next = lc;
56 lc.next = null;
57 ListNode ma = new ListNode(4);
58 ListNode mb = new ListNode(6);
59 ListNode mc = new ListNode(7);
60 ma.next = mb;
61 mb.next = mc;
62 mc.next = null;
63 ListNode root = new MergeList().Merge(la,ma);
64 while(root!=null){
65 System.out.print(root.val + " ");
66 root = root.next;
67 }
68 }
69 }
70 public class ListNode {
71 int val;
72 ListNode next = null;
73
74 ListNode(int val) {
75 this.val = val;
76 }
77 }
1 //递归
2 if(list1 == null)
3 return list2;
4 if(list2 == null)
5 return list1;
6 if(list1.val <= list2.val){
7 list1.next = Merge(list1.next, list2);
8 return list1;
9 }else{
10 list2.next = Merge(list1, list2.next);
11 return list2;
12 }
