题目

In a factory a printer prints labels for boxes. For one kind of boxes the printer has to use colors which, for the sake of simplicity, are named with letters from a to m.

The colors used by the printer are recorded in a control string. For example a “good” control string would be aaabbbbhaijjjm meaning that the printer used three times color a, four times color b, one time color h then one time color a…

Sometimes there are problems: lack of colors, technical malfunction and a “bad” control string is produced e.g. aaaxbbbbyyhwawiwjjjwwm with letters not from a to m.

You have to write a function printer_error which given a string will output the error rate of the printer as a string representing a rational whose numerator is the number of errors and the denominator the length of the control string. Don’t reduce this fraction to a simpler expression.

The string has a length greater or equal to one and contains only letters from ato z.

Examples:

s="aaabbbbhaijjjm"
error_printer(s) => "0/14"

s="aaaxbbbbyyhwawiwjjjwwm"
error_printer(s) => "8/22"

代码

using System;
public class Printer 
{
    public static string PrinterError(String s) 
    {
        int count=0;
        for(int i=0;i<s.Length;i++){
          char c=s[i];
          if(c>'m') count++;
        }
        return string.Format("{0}/{1}",count,s.length);
    }
}

解题思路

本题涉及到字母顺序与数字的关系，以及字符串输出的格式。
1. String.Format Method
https://docs.microsoft.com/zh-cn/dotnet/api/system.string.format?redirectedfrom=MSDN&view=netframework-4.7.2
2. 由题意可知m之后的字母都算是错误的，因此，让字符串中的字符c大于’m’即可找出所有排在m之后的字母。