实现两个链表相加生成新链表

 1 // 将两个链表相加生成新链表
 2 public static Node addTwoNumbers(Node l1, Node l2) {
 3     if (l1 == null) return l2;
 4     if (l2 == null) return l1;
 5 
 6     // 反转链表
 7     l1 = reverseList(l1);
 8     l2 = reverseList(l2);
 9 
10     Node dummyHead = new Node(0);
11     Node current = dummyHead;
12     int carry = 0;
13 
14     while (l1 != null || l2 != null || carry != 0) {
15         int sum = (l1 != null ? l1.val : 0) + (l2 != null ? l2.val : 0) + carry;
16         carry = sum / 10;
17         current.next = new Node(sum % 10);
18         current = current.next;
19 
20         if (l1 != null) l1 = l1.next;
21         if (l2 != null) l2 = l2.next;
22     }
23 
24     // 再次反转结果链表以恢复正确顺序
25     return reverseList(dummyHead.next);
26 }
27 
28 private static Node reverseList(Node head) {
29     Node prev = null;
30     Node current = head;
31     while (current != null) {
32         Node nextTemp = current.next;
33         current.next = prev;
34         prev = current;
35         current = nextTemp;
36     }
37     return prev;
38 }