using System;
using System.Linq;
using System.Collections.Generic;
public class Test
{
public static void Main()
{
var List1=new[] {"123456", "432978", "321675", "321675" };
var List2 = new[] { "7674543897", "1234568897", "8899776644" };
var match = from str1 in List1
join str2 in List2
on str1 equals (str2.Length < 6 ? str2 : str2.Substring(0, 6))
select str2;
foreach(string s2 in match)Console.WriteLine(s2);
}
}
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