LeetCode/21_mergeTwoLists.cpp at master · Derrickers/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) {
        if(!l1)
            return l2;
        if(!l2)
            return l1;
        ListNode *head,*pre,*p;
        if(l1->val<l2->val){
            p = new ListNode(l1->val);
            l1 = l1->next;
        }else{
            p = new ListNode(l2->val);
            l2 = l2->next;
        }
        head = p;
        pre = p;
        while(l1&&l2){
            if(l1->val<l2->val){
                p = new ListNode(l1->val);
                l1 = l1->next;
            }else{
                p = new ListNode(l2->val);
                l2 = l2->next;
            }
            pre->next = p;
            pre = p;
        }
        if(l1)
            pre->next = l1;
        if(l2)
            pre->next = l2;
        return head;
    }
};