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.

用了一个dumb head,。对于这种header不确定的list，可以用dumb header，代码会整洁不少。

/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode dumHeader = new ListNode(0);
ListNode current = dumHeader;
while(l1 != null && l2 != null){
ListNode nextNode = null;
if(l1.val > l2.val){
nextNode = l2;
l2 = l2.next;
current.next = nextNode;
current = nextNode;
}
else if(l2.val >= l1.val){
nextNode = l1;
l1 = l1.next;
current.next = nextNode;
current = nextNode;
}
}

if(l1 != null){
current.next = l1;
}
else if (l2 != null){
current.next = l2;
}

return dumHeader.next;
}
}