Preface
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As the Title Says
Merge two ascending-sorted linked lists into a new ascending linked list and return it. The new list is made by splicing together all the nodes of the two given lists.
Example 1
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输入：l1 = [1,2,4], l2 = [1,3,4]
输出：[1,1,2,3,4,4]
Example 2
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输入：l1 = [], l2 = []
输出：[]
Example 3
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输入：l1 = [], l2 = [0]
输出：[0]
Answer
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struct ListNode {
int val;
ListNode *next;
ListNode() : val(0), next(nullptr) {}
ListNode(int x) : val(x), next(nullptr) {}
ListNode(int x, ListNode *next) : val(x), next(next) {}
};
class Solution {
public:
ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
if (list1 == nullptr) {
return list2;
} else if (list2 == nullptr) {
return list1;
} else if (list1->val < list2->val) {
list1->next = mergeTwoLists(list1->next, list2);
return list1;
} else {
list2->next = mergeTwoLists(list2->next, list1);
return list2;
}
}
};