Add step5

Author: colorbox

2/step5.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+  ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
+    ListNode sentinel_node;
+    ListNode* previous_node = &sentinel_node;
+    int carry = 0;
+    while (l1 || l2 || carry) {
+      int digit = 0;
+      if (l1) {
+        digit += l1->val;
+        l1 = l1->next;
+      }
+      if (l2) {
+        digit += l2->val;
+        l2 = l2->next;
+      }
+      digit += carry;
+      carry = digit / 10;
+      previous_node->next = new ListNode(digit % 10);
+      previous_node = previous_node->next;
+    }
+    return sentinel_node.next;
+  }
+};