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
        Stack<ListNode> stack = new Stack<>();
        ListNode node = head;
        while (null != node) {
            stack.push(node);
            node = node.next;
        }
        int carryBit = 1;
        while (!stack.isEmpty()) {
            node = stack.pop();
            int tmp = node.val + carryBit;
            node.val = tmp % 10;
            carryBit = tmp / 10;
        }
        ListNode res = null;
        if (carryBit == 1) {
            res = new ListNode(1);
            res.next = head;
        }
        else {
            res = head;
        }
        return res;
    }
}