面试题：合并两个排序的链表

Posted 2020-12-31 aaron12

题目描述：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。

方法1：递归

public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        if(list1.val<=list2.val){
            list1.next=Merge(list1.next,list2);
            return list1;
        }else{
            list2.next=Merge(list1,list2.next);
            return list2;
        }
    }
}

方法2：循环

public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        ListNode mergeList=null;
        ListNode current=null;
        while(list1!=null&&list2!=null){
            if(list1.val<=list2.val){
                if(mergeList==null)
                    mergeList=current=list1;
                else{
                    current.next=list1;
                    current=current.next;
                }
                list1=list1.next;
            }else{
                if(mergeList==null)
                    mergeList=current=list2;
                else{
                    current.next=list2;
                    current=current.next;
                }
                list2=list2.next;
            }
        }
        if(list1==null){
            current.next=list2;
        }else{
            current.next=list1;
        }
        return mergeList;
    }
}