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。
/*
public class ListNode {
int val;
ListNode next = null;
ListNode(int val) {
this.val = val;
}
}*/
//合并到root.next
public class Solution {
public ListNode Merge(ListNode list1,ListNode list2) {
if(list1 == null){
return list2;
}
if(list2 == null){
return list1;
}
ListNode root = new ListNode(0);
ListNode pointer = root;
while(list1 != null && list2 != null){
if(list1.val <= list2.val){
pointer.next = list1;
list1 = list1.next;
}else{
pointer.next = list2;
list2 = list2.next;
}
pointer = pointer.next;
}
if(list1 != null){
pointer.next = list1;
}
if(list2 != null){
pointer.next = list2;
}
return root.next;
}
}
