剑指offer五:

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;
    }
}*/
public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {

        ListNode head = new ListNode(-1);
        head.next = null;
        ListNode root = head;
        while(list1 != null && list2 != null){
            if(list1.val < list2.val){
                head.next = list1;
                 head = list1;
                list1 = list1.next;

            }else{
                head.next = list2;
                 head = list2;
                  list2 = list2.next;

            }
        }
        if(list1 == null && list2 != null){
            head.next = list2;
        }
        if(list2 == null && list1 != null){
            head.next = list1;
        }

        return root.next;
    }
}