class Solution

{

public:

  ListNode *mergeTwoLists(ListNode *l1, ListNode *l2)

  { //1 2 4 . 1 3 4

    ListNode *res = new ListNode();

    ListNode *cur = res;

    while (l1 != NULL && l2 != NULL)

    {

      if (l1->val <= l2->val)

      {

        cur->next = l1;

        l1 = l1->next;

        cur = cur->next;

      }

      else

      {

        cur->next = l2;

        l2 = l2->next;

        cur = cur->next;

      }

    }

    if (l1 != NULL)

      cur->next = l1;

    else

      cur->next = l2;

    return res->next;

  }

};