/*
* 21. Merge Two Sorted Lists
* 2016-4-16 By Mingyang
* 开始给出merge two的通用做法,后面再变为merge k的做法
*/
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1==null&&l2==null)
return null;
if(l1==null||l2==null)
return l1==null?l2:l1;
ListNode pre=new ListNode(-1);
ListNode r=pre;
while(l1!=null&&l2!=null){
if(l1.val<l2.val){
r.next=l1;
r=r.next;
l1=l1.next;
}else{
r.next=l2;
r=r.next;
l2=l2.next;
}
}
if(l1!=null)
r.next=l1;
if(l2!=null)
r.next=l2;
return pre.next;
}
// 方法2:上面我们写的代码略多,我们接下来简化一下吧,这样代码更简单,时间更短
public ListNode mergeTwoLists1(ListNode l1, ListNode l2) {
if(l1==null) return l2;
if(l2==null) return l1;
if(l1.val<l2.val){
l1.next=mergeTwoLists(l1.next,l2);
return l1;
}else{
l2.next=mergeTwoLists(l1,l2.next);
return l2;
}
}