LeetCode-Questions/Problem-21 at main · MohdMusaiyab/LeetCode-Questions · GitHub

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/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        ListNode *head=NULL;
        ListNode *tail=NULL;
        ListNode *t1=list1;
        ListNode *t2=list2;
        while(t1!=NULL && t2!=NULL)
        {
            if(head==NULL)
            {
                if(t1->val <= t2->val)
                {
                    head=t1;
                    tail=t1;
                    t1=t1->next;

                }
                else{
                        head=t2;
                        tail=t2;
                        t2=t2->next;
                }
            }
            else{
                    if(t1->val <= t2->val)
                {
                    tail->next=t1;
                    tail=t1;
                    t1=t1->next;
                }
                else{
                        tail->next=t2;
                        tail=t2;
                        t2=t2->next;
                }
            }
        }
             if (t1 != nullptr) {
            if (head == nullptr) {
                head = t1;
            } else {
                tail->next = t1;
            }
        }

        if (t2 != nullptr) {
            if (head == nullptr) {
                head = t2;
            } else {
                tail->next = t2;
            }
        }
return head;
    }
};