2 - Add two numbers, Medium
- Idea is to add given no.s as traverse
- we must take care of the case that if sum > 10, we will have to use an extra variable
carry.
- what if at the end a two digit no. remained like 12, 1 will be added within
while(condition1 && condition2)
for the digit 2, extra if condition is added at the end.
Code
```cpp
ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
ListNode* head = nullptr;
ListNode* tail = head;
int carry = 0;
while (l1 != nullptr or l2 != nullptr) {
int current = 0;
if (l1 != nullptr and l2 != nullptr) {
current = l1 -> val + l2 -> val + carry;
carry = current / 10;
current %= 10;
}
else if (l1 != nullptr) {
current = l1 -> val + carry;
carry = current / 10;
current %= 10;
}
else {
current = l2 -> val + carry;
carry = current / 10;
current %= 10;
}
ListNode *temp = new ListNode;
temp -> val = current;
temp -> next = nullptr;
if (head == nullptr) {
head = tail = temp;
} else {
tail -> next = temp;
tail = temp;
}
if (l1 != nullptr) l1 = l1 -> next;
if (l2 != nullptr) l2 = l2 -> next;
}
if (carry) {
ListNode *temp = new ListNode;
temp -> val = carry;
temp -> next = nullptr;
tail -> next = temp;
tail = temp;
}
return head;
}
```