LintCode_165_合并两个排序链表

1->3->8->11->15->null

2->null

1->2->3->8->11->15->null

/**
* Definition for ListNode.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int val) {
*         this.val = val;
*         this.next = null;
*     }
* }
*/
public class Solution {
/**
* @param ListNode l1 is the head of the linked list
* @param ListNode l2 is the head of the linked list
* @return: ListNode head of linked list
*/
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
// write your code here
if(l1 == null || l2 == null){//如果为空 返回另一个
return l1==null?l2:l1;
}

ListNode small;//取较小的作为头节点
if(l1.val > l2.val){
small = l2;
l2 = l2.next;
}else{
small = l1;
l1 = l1.next;
}
ListNode merge = small;//设定要返回的头节点
while(l1!=null && l2!= null ){
if(l1.val > l2.val){
small.next = l2;
l2 = l2.next;
}else{
small.next = l1;
l1 = l1.next;
}
small = small.next;//指向下一个
}

if(l1 == null){//将非空的剩下的排在后面
small.next = l2;
}else{
small.next = l1;
}

return merge;

}
}

/**
* Definition for ListNode.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int val) {
*         this.val = val;
*         this.next = null;
*     }
* }
*/
public class Solution {
/**
* @param ListNode l1 is the head of the linked list
* @param ListNode l2 is the head of the linked list
* @return: ListNode head of linked list
*/
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
// write your code here
if(l1==null)return l2;
if(l2==null)return l1;
if(l1.val>l2.val){
l2.next=mergeTwoLists(l1,l2.next);
return l2;
}
else{
l1.next=mergeTwoLists(l1.next,l2);
return l1;
}
}
}