两数相加，做了一半

addTwoNumbers.cpp

@@ -0,0 +1,75 @@
+#include <iostream>
+
+using namespace std;
+
+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 *l3 = new ListNode();
+        ListNode *begin = l3;
+        int carry = 0;
+        while (1) {
+            if (l1 == nullptr && l2 == nullptr) {
+                return begin;
+            } else if (l1 == nullptr) {
+                l3->val = l2->val + carry;
+                l2 = l2->next;
+                if (l3->val > 10) {
+                    carry = 1;
+                    l3->val -= 10;
+                } else {
+                    carry = 0;
+                }
+                if (l2->next == nullptr) {
+                    return begin;
+                } else {
+                    l3->next = new ListNode();
+                    l3 = l3->next;
+                }
+            } else if (l2 == nullptr) {
+                l3->val = l1->val + carry;
+                l1 = l1->next;
+                if (l3->val > 10) {
+                    carry = 1;
+                    l3->val -= 10;
+                } else {
+                    carry = 0;
+                }
+                if (l1->next == nullptr) {
+                    return begin;
+                } else {
+                    l3->next = new ListNode();
+                    l3 = l3->next;
+                }
+            } else {
+                l3->val = l1->val + l2->val + carry;
+
+                if (l3->val >= 10) {
+                    carry = 1;
+                    l3->val -= 10;
+                } else {
+                    carry = 0;
+                }
+                
+                l1 = l1->next;
+                l2 = l2->next;
+                l3->next = new ListNode();
+                l3 = l3->next;
+            }
+        }
+    }
+};
+
+int main()
+{
+}