# 21. Merge Two Sorted Lists

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
``````

Thoughts:

1. Recursively find the current least value between two sorted lists and link the next node of the smallest among the rest.

Code:

``````/**
* 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) {
if(!l1) return l2;
if(!l2) return l1;

if(l1->val < l2 -> val){
l1 -> next = mergeTwoLists(l1->next, l2);
return l1;
}
else{
l2->next = mergeTwoLists(l1, l2->next);
return l2;
}
}
};
``````

Code: (Less intuitive way, Java)

``````public class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if (l1 == null) return l2;
if (l2 == null) return l1;

ListNode former=null;
while (l1!=null&&l2!=null) {
if (l1.val>l2.val) {
if (former==null) former=l2; else former.next=l2;
l2=l2.next;
} else {
if (former==null) former=l1; else former.next=l1;
l1=l1.next;
}
}
if (l2!=null) l1=l2;
former.next=l1;