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21_Merge_Two_Sorted_Lists.cpp
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21_Merge_Two_Sorted_Lists.cpp
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// https://leetcode.com/problems/merge-two-sorted-lists/
// https://leetcode.com/problems/merge-two-sorted-lists/discuss/1881644/C%2B%2B-Iterative-Code-or-4ms-Fast
#include <iostream>
using namespace std;
// 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) {}
};
ListNode *mergeTwoLists(ListNode *list1, ListNode *list2)
{
if (list1 == NULL and list2 == NULL)
return NULL;
if (list1 == NULL)
return list2;
if (list2 == NULL)
return list1;
ListNode *first = NULL, *last = NULL;
if (list1->val < list2->val)
{
first = list1;
last = list1;
list1 = list1->next;
last->next = NULL;
}
else
{
first = list2;
last = list2;
list2 = list2->next;
last->next = NULL;
}
while (list1 != NULL and list2 != NULL)
{
if (list1->val < list2->val)
{
last->next = list1;
last = list1;
list1 = list1->next;
last->next = NULL;
}
else
{
last->next = list2;
last = list2;
list2 = list2->next;
last->next = NULL;
}
}
if (list1 != NULL)
last->next = list1;
else if (list2 != NULL)
last->next = list2;
return first;
}
int main()
{
ListNode *head = new ListNode(1);
head->next = new ListNode(2);
head->next->next = new ListNode(3);
head->next->next->next = new ListNode(4);
head->next->next->next->next = new ListNode(5);
ListNode *head2 = new ListNode(1);
head2->next = new ListNode(2);
head2->next->next = new ListNode(3);
head2->next->next->next = new ListNode(4);
head2->next->next->next->next = new ListNode(5);
ListNode *head3 = mergeTwoLists(head, head2);
while (head3 != NULL)
{
cout << head3->val << " -> ";
head3 = head3->next;
}
cout << "NULL" << '\n';
return 0;
}