【leetcode】Merge Two Sorted Lists（easy）

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.

 

思路：使用伪头部

class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        ListNode fakehead(0);
        ListNode *p1 = l1;
        ListNode *p2 = l2;
        ListNode *pnew = &fakehead;

        while(p1 != NULL && p2 != NULL)
        {
            if(p1->val < p2->val)
            {
                pnew->next = p1;
                p1 = p1->next;
            }
            else
            {
                pnew->next = p2;
                p2 = p2->next;
            }
            pnew = pnew->next;
        }
        if(p1 != NULL)
        {
            pnew->next = p1;
        }
        if(p2 != NULL)
        {
            pnew->next = p2;
        }

        return fakehead.next;
    }
};