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| class Solution { public: ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) { if(!list1)return list2; else if (!list2)return list1; auto tk = new ListNode(-1),dumy = tk; while(list1||list2){ if(!list1){ tk = tk->next = list2; break; } else if(!list2){ tk = tk->next = list1; break; } if(list1->val<list2->val){ tk = tk->next = new ListNode(list1->val); list1 = list1->next; } else { tk = tk->next = new ListNode(list2->val); list2= list2->next; } } return dumy->next; } };
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