LEETCODE算法:21. Merge Two Sorted Lists

发表于 更新于 分类于 Waline： 阅读次数：

题目

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4 Output: 1->1->2->3->4->4

题解

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode* ans=NULL,*last=NULL;
        while(l1||l2)
        {
            ListNode* tmp=NULL;
            if(l1&&l2)
            {
                if(l1->val<l2->val)
                {
                    tmp=new ListNode(l1->val);
                    l1=l1->next;
                }else{
                    tmp= new ListNode(l2->val);
                    l2=l2->next;
                }
            }else if(l1){
                tmp=new ListNode(l1->val);
                l1=l1->next;
            }else{
                tmp=new ListNode(l2->val);
                l2=l2->next;
            }
            if(ans==NULL){
                ans=tmp;
                last=tmp;
            } 
            else{
                last->next=tmp;
                last=tmp;
            }
        }
        return ans;
    }
};
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
//判断拿出来节约时间
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode* ans=NULL,*last=NULL;
        while(l1&&l2)
        {
            ListNode* tmp=NULL;
            if(l1->val<l2->val)
            {
                tmp=new ListNode(l1->val);
                l1=l1->next;
            }else{
                tmp= new ListNode(l2->val);
                l2=l2->next;
            }
            if(ans==NULL){
                ans=tmp;
                last=tmp;
            } 
            else{
                last->next=tmp;
                last=tmp;
            }
        }
        while(l1)
        {
            ListNode *tmp=new ListNode(l1->val);
            l1=l1->next;
            if(ans==NULL){
                ans=tmp;
                last=tmp;
            } 
            else{
                last->next=tmp;
                last=tmp;
            }
        }
        while(l2)
        {
            ListNode *tmp=new ListNode(l2->val);
            l2=l2->next;
            if(ans==NULL){
                ans=tmp;
                last=tmp;
            } 
            else{
                last->next=tmp;
                last=tmp;
            }
        }
        return ans;
    }
};