Merge Two Sorted Lists

Desicription

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.

Solution

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/**
* 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 && !l2)
return NULL;
ListNode* head = new ListNode(0);
ListNode* travel = head;
while(l1 || l2){
travel->next = new ListNode(0);
if(!l1 || (l1 && l2 && l2->val <= l1->val)){
travel->val = l2->val;
l2 = l2->next;
if(!l1 && !l2)
travel->next = NULL;
travel = travel->next;
}
else if(!l2 || (l1 && l2 && l2->val > l1->val)){
travel->val = l1->val;
l1 = l1->next;
if(!l1 && !l2)
travel->next = NULL;
travel = travel->next;
}
}
return head;
}
};