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.

Solutions:

/**
 * 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;
        ListNode* head;
        ListNode* temp;
        if(l1->val < l2->val)
        {
            head = l1;
            temp = l2;
        }
        else
        {
            head = l2;
            temp = l1;
        }
        ListNode* temp1 = head->next;
        ListNode* now = head;
        while(temp1!=NULL && temp!=NULL)
        {
            if(temp1->val > temp->val)
            {
                now->next = temp;
                now = now->next;
                temp = temp->next;
            }
            else
            {
                now->next = temp1;
                now = now->next;
                temp1 = temp1->next;
            }
        }
        if(temp1 == NULL)
            now->next = temp;
        if(temp == NULL)
            now->next = temp1;
        return head;
    }
};

LeetCode--Merge Two Sorted Lists