refactor 2

fishercoder1534 · fishercoder1534 · commit 1bfd15f313ef · 2021-10-24T09:30:17.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_2.java b/src/main/java/com/fishercoder/solutions/_2.java
@@ -4,12 +4,15 @@
 
 public class _2 {
     public static class Solution1 {
+        /**
+         * My completely original solution on 10/24/2021.
+         */
         public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
-            ListNode result = new ListNode(0);
-            ListNode tmp = result;
-            int sum = 0;
+            int carry = 0;
+            ListNode pre = new ListNode(-1);
+            ListNode tmp = pre;
             while (l1 != null || l2 != null) {
-                sum /= 10;
+                int sum = 0;
                 if (l1 != null) {
                     sum += l1.val;
                     l1 = l1.next;
@@ -18,13 +21,15 @@ public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
                     sum += l2.val;
                     l2 = l2.next;
                 }
+                sum += carry;
                 tmp.next = new ListNode(sum % 10);
                 tmp = tmp.next;
+                carry = sum / 10;
             }
-            if (sum / 10 == 1) {
-                tmp.next = new ListNode(1);//this means there's a carry, so we add additional 1, e.g. [5] + [5] = [0, 1]
+            if (carry != 0) {
+                tmp.next = new ListNode(carry);
             }
-            return result.val == 0 ? result.next : result;
+            return pre.next;
         }
     }
 
