merge_2_sorted.cpp

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        ListNode* dummy = new ListNode(-1);
        ListNode* ptr1 = list1;
        ListNode* ptr2 = list2;
        ListNode* ptr3 = dummy;
        while(ptr1!=NULL && ptr2!=NULL){
            if(ptr1->val<ptr2->val){
                ptr3->next=ptr1;
                ptr1=ptr1->next;
            }
            else if(ptr1->val>=ptr2->val){
                ptr3->next=ptr2;
                ptr2=ptr2->next;
            }
            ptr3=ptr3->next;
        }
        while(ptr1!=NULL){
            ptr3->next=ptr1;
            ptr1=ptr1->next;
            ptr3=ptr3->next;
        }
        while(ptr2!=NULL){
            ptr3->next=ptr2;
            ptr2=ptr2->next;
            ptr3=ptr3->next;
        }
        return dummy->next;
    }
};