题解 | #给单链表加一#

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 head ListNode类
     * @return ListNode类
     */
    public ListNode plusOne (ListNode head) {
        // write code here
        if (head == null)
            return head;
        //倒序
        ListNode ln = new ListNode(0);
        while (head != null) {
            ListNode lnT = ln.next;
            ln.next = head;
            head = head.next;
            ln.next.next = lnT;
        }
        ListNode lnTG = ln.next;
        int nAddc = 1;
        ListNode lnR = ln;
        lnR.next = null;
        while (lnTG != null) {
            int nT = lnTG.val;
            lnTG.val = (nT + nAddc) % 10;
            nAddc = (nT + nAddc) / 10;
            ListNode lnT = lnR.next;
            lnR.next = lnTG;
            ListNode lnTGN = lnTG.next;
            lnTG.next = lnT;
            lnTG = lnTGN;
        }
        if (nAddc > 0) {
            ln.val = 1;
            return ln;
        } else {
            return ln.next;
        }
    }
}