[面试真题] LeetCode：Merge Two Sorted Lists

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.

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode *head = new ListNode(0);
        ListNode *tail = head;
        ListNode *a = l1;
        ListNode *b = l2;
        while(a || b){
            if(a && b && a->val < b->val){
                tail->next = a;
                a = a->next;
            }else if (a && b && a->val > b->val){
                tail->next = b;
                b = b->next;
            }else if(a){
                tail->next = a;
                a = a->next;
            }else{
                tail->next = b;
                b = b->next;
            }
            tail = tail->next;
        }
        return head->next;
    }
};

Run Status: Accepted!
Program Runtime: 56 milli secs

Progress: 208/208 test cases passed.