2. Add Two Numbers(https://leetcode.com/problems/add-two-numbers/)

Author: guolanren

src/main/java/name/guolanren/_1to100/_1to10/p2/AddTwoNumbers.java

@@ -7,67 +7,32 @@
 public class AddTwoNumbers {
 
     public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
-        ListNode sumListNode = l1;
-        ListNode currentNode = sumListNode;
-        ListNode prevNode = null;
-        int carry = 0;
-        while (true) {
-            // l1 遍历完了，将 l2 加上进位后，接到 sumListNode 尾
-            if (l1 == null) {
-                prevNode.next = withCarry(l2, carry);
-                break;
+        ListNode l3 = new ListNode();
+        ListNode tail = l3;
+        int nodeVal = 0;
+        while (l1 != null || l2 != null || nodeVal != 0) {
+            if (l1 != null) {
+                nodeVal += l1.val;
+                l1 = l1.next;
             }
-            // l2 遍历完了，将 l1 加上进位后，接到 sumListNode 尾
-            if (l2 == null) {
-                prevNode.next = withCarry(l1, carry);
-                break;
-            }
-
-            // 计算当前节点值
-            currentNode.val = l1.val + l2.val + carry;
 
-            // 是否需要进位
-            if (currentNode.val > 9) {
-                currentNode.val -= 10;
-                carry = 1;
-            } else {
-                carry = 0;
+            if (l2 != null) {
+                nodeVal += l2.val;
+                l2 = l2.next;
             }
 
-            l1 = l1.next;
-            l2 = l2.next;
-            prevNode = currentNode;
-            currentNode = currentNode.next;
+            tail.next = new ListNode(nodeVal % 10);
+            tail = tail.next;
+            nodeVal = nodeVal / 10;
         }
-        return sumListNode;
+        return l3.next;
     }
+}
 
-    /**
-     * ListNode 加上进位
-     */
-    private ListNode withCarry(ListNode l, int carry) {
-        ListNode head = l;
-        if (l != null) {
-            while (true) {
-                l.val += carry;
-
-                if (l.val < 10) {
-                    break;
-                }
-
-                l.val -= 10;
-                carry = 1;
-
-                if (l.next == null) {
-                    l.next = new ListNode(carry);
-                    break;
-                }
-
-                l = l.next;
-            }
-        } else if (carry > 0) {
-            return new ListNode(carry);
-        }
-        return head;
-    }
+class ListNode {
+    int val;
+    ListNode next;
+    ListNode() {}
+    ListNode(int val) { this.val = val; }
+    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 }