题目

Take 2 strings s1 and s2 including only letters from ato z. Return a new sorted string, the longest possible, containing distinct letters,

each taken only once – coming from s1 or s2.

Examples

a = "xyaabbbccccdefww"
b = "xxxxyyyyabklmopq"
longest(a, b) -> "abcdefklmopqwxy"

a = "abcdefghijklmnopqrstuvwxyz"
longest(a, a) -> "abcdefghijklmnopqrstuvwxyz"

代码

using System;
using System.Linq;
public class TwoToOne 
{

  public static string Longest (string s1, string s2) 
  {
      string ss="";
      var ordered1=s1.OrderBy(c=>c);
      var ordered2=s2.OrderBy(c=>c);
      string ns1=new string(ordered1.ToArray());
      string ns2=new string(ordered2.ToArray());
      //s1或s2等于空的情况
      if(ns1==""){
        foreach(char c in s2){
        if(!ss.Contains(c)){ss+=c;}
        }
        return ss;
      }
      if(ns2==""){
        foreach(char c in s1){
        if(!ss.Contains(c)){ss+=c;}
        return ss;
        }
      }
      //s1、s2不为空
      for(int i=0;i<ns1.Length;i++){
        char c1=ns1[i];      
        if(!ss.Contains(c1)){ss+=c1;}       
      }    
      for(int i=0;i<ns2.Length;i++){
         char c2=ns2[i];
         if(!ss.Contains(c2)){ss+=c2;}
      }
      var ordered3=ss.OrderBy(c=>c);
      string output=new string(ordered3.ToArray());
      return output;
  }
}

（别人的）简洁写法

Linq真的很方便，然而我用得还不够熟练。

using System.Linq;

public class TwoToOne 
{
  public static string Longest (string s1, string s2) 
  {
     return new string ((s1 +s2).Distinct().OrderBy(x=>x).ToArray ());
  }
}

参考资料

1. Enumerable.Distinct Method
   https://docs.microsoft.com/zh-cn/dotnet/api/system.linq.enumerable.distinct?view=netframework-4.8
   提供一组用于查询实现 IEnumerable 的对象的 static 方法。