题解 | #链表相加(二)#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head1 ListNode类
     * @param head2 ListNode类
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        // write code here
        int a = 0, b = 0;
        if (head1 == null) {
            return head2;
        }
        if (head2 == null) {
            return head1;
        }
        ListNode virtualHead1 = new ListNode(0);
        virtualHead1.next = head1;
        ListNode prev = virtualHead1;
        ListNode cur = head1;
        ListNode next = head1.next;
        ListNode newHead1 = head1, newHead2 = head2;

        while (head1.next != null) {
            ListNode t = head1.next;
            head1.next = head1.next.next;
            t.next = newHead1;
            newHead1 = t;
        }
        while (head2.next != null) {
            ListNode t = head2.next;
            head2.next = head2.next.next;
            t.next = newHead2;
            newHead2 = t;
        }
        ListNode heading = new ListNode(0);
        int nextIncr = 0;
        while (newHead1 != null || newHead2 != null) {
            int val = (newHead1 == null ? 0 : newHead1.val) + (newHead2 == null ? 0 :
                      newHead2.val) + nextIncr;
            int remaining = val % 10;
            nextIncr = val / 10;

            ListNode t = new ListNode(remaining);
            t.next = heading.next;
            heading.next = t;

            newHead1 = newHead1 == null ? null : newHead1.next;
            newHead2 = newHead2 == null ? null : newHead2.next;
        }
        if (nextIncr > 0) {
            ListNode t = new ListNode(nextIncr);
            t.next = heading.next;
            heading.next = t;
        }

        return heading.next;

    }
}