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) {
        // write code here
        ListNode newHead = new ListNode(-1);
        ListNode newTail = newHead;
        ListNode pre1 = null;
        ListNode pre2 = null;
        ListNode cur1 = head1;
        ListNode cur2 = head2;
        while (cur1 != null) {
            ListNode next1 = cur1.next;
            cur1.next = pre1;
            pre1 = cur1;
            cur1 = next1;
        }
        while (cur2 != null) {
            ListNode next2 = cur2.next;
            cur2.next = pre2;
            pre2 = cur2;
            cur2 = next2;
        }
        int flag = 0;
        while (pre1 != null && pre2 != null) {
            int sum = pre1.val + pre2.val + flag;
            flag = sum / 10;
            ListNode node = new ListNode(sum % 10);
            newTail.next = node;
            newTail = newTail.next;
            pre1 = pre1.next;
            pre2 = pre2.next;
        }
        if (pre1 == null && pre2 == null && flag != 0) {
            ListNode temp = new ListNode(flag);
            newTail.next = temp;
        }
        while (pre1 != null) {
            int sum = pre1.val + flag;
            flag = sum / 10;
            ListNode node = new ListNode(sum % 10);
            newTail.next = node;
            newTail = newTail.next;
            pre1 = pre1.next;
        }
        while (pre2 != null) {
            int sum = pre2.val + flag;
            flag = sum / 10;
            ListNode node = new ListNode(sum % 10);
            newTail.next = node;
            newTail = newTail.next;
            pre2 = pre2.next;
        }
        if (flag != 0) {
            ListNode node = new ListNode(flag);
            newTail.next = node;
        }
        ListNode pre3 = null;
        ListNode cur3 = newHead.next;
        while (cur3 != null) {
            ListNode next3 = cur3.next;
            cur3.next = pre3;
            pre3 = cur3;
            cur3 = next3;
        }
        return pre3;
    }
}