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mege_sorted_list.cpp
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mege_sorted_list.cpp
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//
// Created by roseduan on 2021/9/20.
// 合并两个有序链表
//
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:
// 迭代法
ListNode* mergeTwoLists1(ListNode* l1, ListNode* l2) {
auto dummy = new ListNode();
auto p = dummy;
while (l1 && l2) {
if (l1->val < l2->val) {
p->next = l1;
l1 = l1->next;
} else {
p->next = l2;
l2 = l2->next;
}
p = p->next;
}
p->next = l1 ? l1 : l2;
return dummy->next;
}
// 递归
ListNode* mergeTwoLists2(ListNode* l1, ListNode* l2) {
if (l1 == nullptr) {
return l2;
}
if (l2 == nullptr) {
return l1;
}
if (l1->val < l2->val) {
l1->next = mergeTwoLists2(l1->next, l2);
return l1;
} else {
l2->next = mergeTwoLists2(l1, l2->next);
return l2;
}
}
};