leetcode：Merge Two Sorted Lists （連結兩個有序鏈表）【面試演算法題】

題目：

/** * 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 *root,*p;        root=new ListNode(-1);        p=root;        while(1)        {            if(l1==NULL){p->next=l2;break;}            if(l2==NULL){p->next=l1;break;}            if(l1->val<l2->val)            {                p->next=l1;                l1=l1->next;            }            else            {                p->next=l2;                l2=l2->next;            }            p=p->next;        }        return root->next;    }};