/**
* 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) {
ListNode *head = NULL, *cur = NULL;
while (l1 && l2) {
if (l1->val <= l2->val) {
if (!head) {
head = cur = l1;
} else {
cur->next = l1;
cur = cur->next;
}
l1 = l1->next;
} else {
if (!head) {
head = cur = l2;
} else {
cur->next = l2;
cur = cur->next;
}
l2 = l2->next;
}
}
if (!head) {
head = cur = l1? l1:l2;
}
else if (cur) {
cur->next = l1? l1:l2;
}
return head;
}
};