题解 | #链表相加(二)#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        ListNode overHead1 = overList(head1);
        ListNode overHead2 = overList(head2);
        ListNode head = new ListNode(0);
        ListNode index = head;
        int carry = 0;
        int sum = 0;
        int val = 0;
        while (overHead1 != null || overHead2 != null) {

            if (overHead1 == null) {
                sum = overHead2.val + carry;
                overHead2 = overHead2.next;
            } else if (overHead2 == null) {
                sum = overHead1.val + carry;
                overHead1 = overHead1.next;
            } else {
                sum = overHead1.val + overHead2.val + carry;
                overHead1 = overHead1.next;
                overHead2 = overHead2.next;
            }
            val = sum % 10;
            carry = sum / 10;
            
            index.next = new ListNode(val);
            index = index.next;
        }
        if (carry != 0) {
            index.next = new ListNode(carry);
            index = index.next; 
        }
        return overList(head.next);
    }

    private ListNode overList(ListNode head) {
        if (head == null) {
            return head;
        }
        ListNode node = null, cur = head;
        while (cur != null) {
            ListNode tail = cur.next;
            cur.next = node;
            node = cur;
            cur = tail;
        }
        return node;
    }
}