leetcode 21 -- Merge Two Sorted Lists
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Merge Two Sorted Lists
题目:
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.
题意:
合并两个排序过的链表
思路:
这是个非经常见的问题,须要注意的就是给定两个链表是否为空。
代码:
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
if(l1 == NULL && l2 == NULL){
return NULL;
}else if(l1 == NULL && l2 != NULL){
return l2;
}else if(l1 != NULL && l2 == NULL){
return l1;
}
//指定头节点
ListNode *new_head = NULL;
if(l1->val < l2->val){
new_head = l1;
l1 = l1->next;
}else{
new_head = l2;
l2 = l2->next;
}
ListNode *p = new_head;
while(l1 != NULL && l2 != NULL){
if(l1->val < l2->val){
p->next = l1;
p = p->next;
l1 = l1->next;
}else{
p->next = l2;
p = p->next;
l2 = l2->next;
}
}
//接上余下的链表段
if(l1 != NULL){
p->next = l1;
}else{
p->next = l2;
}
return new_head;
}
};
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