【面试题17】合并两个排序的链表

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。

递归实现：

非递归方式：

public class Solution {

    public ListNode Merge(ListNode list1,ListNode list2) {

        if (list1 ==null)

            return list2;

        if (list2 ==null)

            return list1;

        ListNode head = null;

        ListNode tmp= null;

        if (list1.val < list2.val)

            {

            head = list1;

                list1 = list1.next;

        }

        else

        {

            head = list2;

                list2 = list2.next;

        }

        tmp = head;

        while (list1 != null && list2 != null)

            {

            if (list1.val < list2.val)

            {

               

            tmp.next = list1;

                list1 = list1.next;

                tmp = tmp.next;

               

        }

        else

        {

           tmp.next = list2;

                list2 = list2.next;

            tmp = tmp.next;

        }

        }

       

         while (list1 != null || list2 != null)

            {

        if (list1 ==null && list2 != null)

            {

            tmp.next = list2;

                list2 = list2.next;

            tmp = tmp.next;

        }

       

         if (list2 ==null && list1 != null)

            {

            tmp.next = list1;

                list1 = list1.next;

            tmp = tmp.next;

        }

         }

        return head;

       

    }

}