21. Merge Two Sorted Lists

题目

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

解析

class Solution_21 {
public:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        if (l1==NULL)
        {
            return l2;
        }
        if (l2==NULL)
        {
            return l1;
        }
        ListNode* head = new ListNode(0);
        ListNode* cur = head;
        while (l1!=NULL&&l2!=NULL)
        {
            if (l1->val<=l2->val)
            {
                cur->next = l1;
                l1 = l1->next;
                cur = cur->next;
            }
            else
            {
                cur->next = l2;
                l2 = l2->next;
                cur = cur->next;
            }
        }
        if (l1!=NULL)
        {
            cur->next = l1;
        }
        if (l2!=NULL)
        {
            cur->next = l2;
        }
        return head->next;
    }
};

题目来源

• 21. Merge Two Sorted Lists