某天下午忙的眼到爆，茶歇的时候突然聊起算法，同事提到写个9宫格键盘下的英文字符全排列。嗯。。。

第二天老哥发来了Python的递归实现，十分精简玄妙。

Challenge Accepted!

我来个循环的吧，直接上代码：

C#循环的实现

using System;
using System.Collections.Generic;

public class Test
{
  public static void Main()
  {
    var test = new Test();
    test.Permutation("234");
    test.Print();
  }

  static Dictionary<string,string> KeyMap = new Dictionary<string,string>{
    {"2","abc"},
    {"3","def"},
    {"4","ghi"},
    {"5","jkl"},
    {"6","mno"},
    {"7","pqrs"},
    {"8","tuv"},
    {"9","wxyz"},
  };
    
  string[] OutPut;
  
  void Permutation(string input)
  {
    var repeatArr = new int[input.Length];
    var inputArr = input.ToCharArray();
    var numberOfCombination = 1;
    
    for(int i = input.Length - 1; i >= 0 ; i--)
    {
      var str = KeyMap[inputArr[i].ToString()];
      repeatArr[i] = numberOfCombination;
      numberOfCombination = numberOfCombination * str.Length;
    }
    
    OutPut = new string[numberOfCombination];

    for(int x = 0; x < input.Length; x++)
    {
      var letterPointer = 0;
      var count = 0;
      var letters = KeyMap[inputArr[x].ToString()];

      for(int y = 0; y < numberOfCombination; y++)
      {    
        var lettersArr = letters.ToCharArray(); 
        var letter = lettersArr[letterPointer];
        
        OutPut[y] += letter.ToString();
        count++;

        if(count == repeatArr[x])
        {
          count = 0;
          letterPointer++;
          if(letterPointer == lettersArr.Length)
          {
            letterPointer = 0;
          }
        }
      }
    }
  }
  
  void Print()
  {
    for(int i = 0; i < OutPut.Length; i++)
    {
      Console.WriteLine(OutPut[i]);
    }
  }

}

挑战达成！

过两天懒劲过了把解析补上嗯嗯，先立flag