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21.cpp
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21.cpp
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/**
* Definition for singly-linked list.
* 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) {
ListNode *curr1 = list1;
ListNode *curr2 = list2;
ListNode *head = nullptr;
if (!curr1 && !curr2) {
return head;
}
ListNode *curr;
while (curr1 || curr2) {
ListNode *newNode = new ListNode();
if (curr1 && curr2 && curr1->val > curr2->val) {
newNode->val = curr2->val;
curr2 = curr2->next;
} else if (curr1 && curr2) {
newNode->val = curr1->val;
curr1 = curr1->next;
} else if (curr1) {
newNode->val = curr1->val;
curr1 = curr1->next;
} else if (curr2) {
newNode->val = curr2->val;
curr2 = curr2->next;
}
if (!head) {
head = newNode;
curr = head;
} else {
curr->next = newNode;
curr = newNode;
}
}
return head;
}
};