LeetCode/C++/21-Merge-Two-Sorted-Lists.cpp at master · Sixzeroo/LeetCode · GitHub

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/**
 * 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 * p= NULL, * pp = NULL;
        if(l1 == NULL)return l2;
        if(l2 == NULL)return l1;
        if(l1->val<l2->val)
        {
            pp = p = l1;
            l1 =l1->next;
        }
        else
        {
            pp =p = l2;
            l2 =l2->next;
        }
        while(l1 != NULL && l2 != NULL)
        {
            if(l1->val < l2->val)
            {
                p -> next = l1;
                l1 = l1->next;

            }
            else
            {
                p -> next = l2;
                l2 = l2->next;
            }
            p = p->next;

        }
        if(l1 != NULL)
        {
            p -> next= l1;
        }
        if(l2 != NULL)
            p -> next= l2;
        return pp ;
    }
};