一个简单的递归面试题

这几天，一直都在找工作，一直都在笔试面试，其中也遇到很多笔试题目，大多都记不清楚了，应该不是很难。

下面分享一个公司给我出的机试题目：要求当m<n时，利用递归实现 m + (m+1) + (m+2) + ... + n

并要求用控制台程序实现，并且当用户输入的参数错误时，提示用户是否要重新输入。

想了一会，写出了如下代码：

?

/*

=============================================================================

作者：音乐让我说

代码描述：一个简单面试题，要求当m<n时，利用递归实现 m + (m+1) + (m+2) + ... + n

谢谢您的支持，欢迎您的转载，转载时请注明，谢谢！

=============================================================================  

*/

 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

 

namespace TempConApp

{

    class Program

    {

        static void Main(string[] args)

        {

            bool isContinue = true;

            do

            {

                Console.WriteLine("\n=======================================================\n");

                bool failedIsContinued;

                long num1;

                if (!GetUserInputNum(1, out num1, out failedIsContinued))

                {

                    isContinue = failedIsContinued;

                    continue;

                }

                long num2;

                if (!GetUserInputNum(2, out num2, out failedIsContinued))

                {

                    isContinue = failedIsContinued;

                    continue;

                }

                if (num1 >= num2)

                {

                    Console.Write("第 1 个数字必须小于第 2 个数字！");

                    isContinue = GetFailedIsContinued();

                    continue;

                }

                long result = GetResult(num1, num2);

                Console.WriteLine("结果为：" + result);

                 

            } while (isContinue);

            Console.WriteLine("程序运行完毕！");

            Console.ReadKey();

        }

 

        /// <summary>

        /// 利用递归，得到从第一个数字到第二个数字之间所有数的总和（最后的总和包括第一个数和第二个数）

        /// </summary>

        /// <param name="beginNum">第一个数</param>

        /// <param name="endNum">第二个数</param>

        /// <returns></returns>

        static long GetResult(long beginNum, long endNum)

        {

            if (beginNum >= endNum)

            {

                return beginNum;

            }

            return endNum + GetResult(beginNum, endNum - 1);

        }

 

        /// <summary>

        /// 得到用户输入的数字

        /// </summary>

        /// <param name="serialNum">数字编号，表明这是输入的第几个数字，第一个调用该方法，传入 1 </param>

        /// <param name="outputNum">返回的值</param>

        /// <param name="failedIsContinued">转换失败后，是否要继续</param>

        /// <returns>返回用户输入的是否是数字，如果是，则返回 true </returns>

        static bool GetUserInputNum(int serialNum, out long outputNum, out bool failedIsContinued)

        {

            bool returnFlag = true;

            failedIsContinued = true;

            Console.Write("请输入第 " + serialNum + " 个数字：");

            string strNum = Console.ReadLine();

            if (!long.TryParse(strNum, out outputNum))

            {

                //转换失败

                returnFlag = false;

                Console.Write("您输入的第 " + serialNum + " 个数字错误！");

                failedIsContinued = GetFailedIsContinued();

            }

            return returnFlag;

        }

 

        /// <summary>

        /// 当失败后，获取用户是否想要继续

        /// </summary>

        /// <returns></returns>

        static bool GetFailedIsContinued()

        {

            Console.Write("是否继续重新输入？(y/n) ：");

            string isContinueWord = Console.ReadLine();

            if (!string.Equals(isContinueWord, "Y", StringComparison.CurrentCultureIgnoreCase))

            {

                //不继续

                return false;

            }

            return true;

        }

    }

}

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