using System;
using System.Collections.Generic;
using System.Linq;
 
public class Test
{
	public static void Main()
	{
	List<string> sourceNames = new List<string>() { "A", "B", "C", "A", "B", "C" };
	List<string> targetNames = new List<string>() { "Z", "Y", "X", "W", "V", "U" };
 
	var lookup = sourceNames
	   .Select((Source, i) => new { Target = targetNames.ElementAt(i), Source})
	   .GroupBy(x => x.Source)
	   .ToDictionary(g => g.Key, g => g.Select(x => x.Target));
 
	foreach(var kv in lookup)
		Console.WriteLine("{0} has destinations {1}"
		, kv.Key
		, string.Join(",", lookup[kv.Key].ToArray()));
	}
}

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