Find longest common contiguous click stream between two user records

LongestContiguousClickstream.cs

var user0 = new string[] { "/a", "/b", "/c", "/d", "/e", "/f" };
var user1 = new string[] { "/b", "/c", "/e", "/f" };
var user2 = new string[] { "/a", "/b", "/d", "/e", "/f" };
var user3 = new string[] { "/a", "/c", "/d", "/e", "/f" };
var user4 = new string[] { "/a", "/b", "/c", "/d", "/e", "/f" };
var user5 = new string[] { "/a", "/b", "/e", "/f" };
var user6 = new string[] { "/a", "/b", "/c", "/e", "/f" };
var user7 = new string[] { "/c", "/d", "/e", "/f" };
var user8 = new string[] { "/d", "/e", "/f" };
var user9 = new string[] { "/b", "/c", "/e", "/f" };

Dictionary<string, string> BuildDictionary(string[] clickStream)
{
	var dict = new Dictionary<string, string>();

	for (var i = 0; i < clickStream.Length; i++)
	{
		dict.Add(
			clickStream[i],
			(i == clickStream.Length - 1
				? string.Empty
				: clickStream[i + 1]));
	}

	return dict;
}

string[] LongestContiguousClickStream(string[] userA, string[] userB)
{
	var dictA = BuildDictionary(userA);
	var dictB = BuildDictionary(userB);
	var shortest = (dictA.Count < dictB.Count ? dictA : dictB);
	var longest = (dictA.Count >= dictB.Count ? dictA : dictB);
	List<string>? longestCommon = null;

	foreach (var url in shortest.Keys)
	{
		if (!longest.ContainsKey(url))
		{
			continue;
		}

		var contiguous = new List<string>();
		var currentUrl = url;
		var nextUrl = shortest[url];

		while (true)
		{
			contiguous.Add(currentUrl);

			if (nextUrl == string.Empty
				|| longest[currentUrl] != nextUrl)
			{
				break;
			}

			currentUrl = nextUrl;
			nextUrl = shortest[nextUrl];
		}

		if (contiguous.Count > (longestCommon?.Count ?? 0))
		{
			longestCommon = contiguous;
		}
	}

	return longestCommon?.ToArray() ?? new string[] { };
}

var result = LongestContiguousClickStream(user3, user4);

Console.WriteLine(string.Join(", ", result));