21. Merge Two Sorted Lists (Easy)
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.
Example:
Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4
solution
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode head = new ListNode(-1);
ListNode p = head, temp = null;
while (l1 != null && l2 != null)
{
if (l1.val > l2.val)
{
temp = l2;
l2 = l2.next;
}
else
{
temp = l1;
l1 = l1.next;
}
p.next = temp;
p = temp;
}
p.next = l1 != null ? l1 : l2;
return head.next;
}
}
总结
题意是给定两个有序链表l1和l2,将这两个链表合并成一个有序链表。我的思路是构造一个头结点head,然后用一个while循环遍历这两个链表,如果l1.val大于l2.val,则将l2结点用temp变量保存起来,然后l2指向下一个结点,否则,则将l1结点用temp变量保存起来,然后l1指向下一个结点;接着使用尾插法将temp结点插到head链表的尾部;循环结束之后,再将剩下的结点直接插入到head链表尾部,最后返回head.next结点。
还有一种思路是用递归,这里就不细说了。
Notes
1.链表的插入,删除操作最好构造一个额外的头结点,方便操作的统一;
2.此题与两个有序数组的合并是一样的思路;