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.
Example:
Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4
Solution:
Iterative: Use a zombie head and a get helper function
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
inline int get(ListNode* l){
return l?l->val:INT_MAX;
}
ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
ListNode* head = new ListNode(0);
ListNode* cur = head;
while(l1 || l2){
if(get(l1)>get(l2)){
swap(l1,l2);
}
cur->next = l1;
cur = cur->next;
l1 = l1->next;
}
return head->next;
}
};
Recursive:
/**
* 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 == NULL) {
return l2;
}
if (l2 == NULL) {
return l1;
}
if (l1->val < l2->val) {
l1->next = mergeTwoLists(l2, l1->next);
return l1;
} else {
l2->next = mergeTwoLists(l2->next, l1);
return l2;
}
}
};