LeetCode第22题--合并两个排序好的链表

LeetCode第22题–合并两个排序好的链表

代码

public class MergeSortedLists {
public class ListNode {
int val;
ListNode next;
ListNode(int x) { val = x; }
}
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode result = null;  //变量在申请之后一定要初始化，否则会报编译错误

//下面是三种特殊的情况，当其中有一个链表为空时，直接返回不为空的一个，如果两个链表全部为空，则返回空
if(l1 == null && l2 != null){
result = l2;
return result;
}

if(l2 == null && l1 != null){
result = l1;
return result;
}

if(l1 == null && l2 == null){
result = null;
return result;
}

result = new ListNode(0);   //创建新的节点
ListNode current = result;   //创建一个当前节点，result的指针不会发生变化，变化的是current
//System.out.println(current.val);
//处理两个链表都不为空的情况
while(l1 != null && l2 != null){
if(l1.val > l2.val){
current.val = l2.val;
l2 = l2.next;
if(l2 == null){
current.next = l1;
break;
}
ListNode temp = new ListNode(0);
current.next = temp;
current = current.next;
}else if(l1.val < l2.val) {
current.val = l1.val;
l1 = l1.next;
if(l1 == null){
current.next = l2;
break;
}
ListNode temp = new ListNode(0);
current.next = temp;
current = current.next;
}else{  //l1.val == l2.val
current.val = l1.val;

ListNode temp = new ListNode(0);
current.next = temp;
current = current.next;
current.val = l2.val;

l1 = l1.next;
l2 = l2.next;
if(l1 == null){
current.next = l2;
break;
}

if(l2 == null){
//System.out.println(l1.val + " " + l1.next.val);
//System.out.println("娃娃");
current.next = l1;
//System.out.println(current.next.val + " " + current.next.next.val);
break;
}

temp = new ListNode(0);
current.next = temp;
current = current.next;

}
}

return result;
}
}