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21. Merge Two Sorted Lists

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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.

思路:跟merge two arrays很像。一一比较大小,小的用dummy node接上,再继续找,继续比较。最后检查下两个list,如果两个list都空了,那就完成了。任何一个linkedlist不空,就把之前建立的接到那个linkedlist搜索到的node上。

/** * 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) {        if(l1==null)        {            return l2;        }        if(l2==null)        {            return l1;        }        ListNode dummy=new ListNode(-1);        ListNode node=dummy;        while(l1!=null&&l2!=null)        {            if(l1.val<l2.val)            {                node.next=l1;                l1=l1.next;            }            else            {                node.next=l2;                l2=l2.next;            }            node=node.next;        }        if(l1!=null)        {            node.next=l1;        }        if(l2!=null)        {            node.next=l2;        }        return dummy.next;    }}

 

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21. Merge Two Sorted Lists