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21. 合并两个有序链表 ​

为保证权益，题目请参考 21. 合并两个有序链表(From LeetCode).

解决方案1 ​

CPP ​

C++
#include <iostream>
using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

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

        if(l1 == NULL)
        {
            while(l2 != NULL)
            {
                head->next = l2;
                head = head->next;
                l2 = l2->next;
                head->next = NULL;
            }
        }
        if(l2 == NULL)
        {
            while(l1 != NULL)
            {
                head->next = l1;
                head = head->next;
                l1 = l1->next;
                head->next = NULL;
            }
        }
        return ans;
    }
};

int main()
{
    return 0;
}