1.描述

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.

2.分析

3.代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 
struct ListNode* mergeTwoLists(struct ListNode* l1, struct ListNode* l2) {
    if (NULL == l1 && NULL == l2) return NULL;
    if (NULL == l1) return l2;
    if (NULL == l2) return l1;
    
    struct ListNode* l3 = l1->val <= l2->val ? l1 : l2;
    if (l1->val <= l2->val) l1 = l1->next;
    else l2 = l2->next;
    struct ListNode* tail = l3;
    
    while (l1 && l2) {
        if (l1->val <= l2->val) {
            tail->next = l1;
            l1 = l1->next;
        } else {
            tail->next = l2;
            l2 = l2->next;
        }
        tail = tail->next;
    }
    tail->next = l1 ? l1 : l2;
    return l3;
}