add task 2

2. Add Two Numbers/solution.cpp

@@ -0,0 +1,34 @@
+/**
+ * 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* addTwoNumbers(ListNode* l1, ListNode* l2) {
+        ListNode* dummy = new ListNode(0);
+        ListNode* cur = dummy;
+        int carry = 0;
+
+        while (l1 != nullptr || l2 != nullptr || carry != 0) {
+            int v1 = (l1 != nullptr) ? l1->val : 0;
+            int v2 = (l2 != nullptr) ? l2->val : 0;
+
+            int sum = v1 + v2 + carry;
+            carry = sum / 10;
+
+            cur->next = new ListNode(sum % 10);
+            cur = cur->next;
+
+            if (l1 != nullptr) l1 = l1->next;
+            if (l2 != nullptr) l2 = l2->next;
+        }
+
+        return dummy->next;
+    }
+};