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namespace _1_no_connection;
public static class NoConnection
{
public static async Task Main()
{
// Read the input, a series of lines in the format "start end", followed by a blank line.
var connections = await Console.In.ReadLinesAsync()
.TakeWhile(line => !string.IsNullOrWhiteSpace(line))
.Select(line => line.Trim().Split(' ', 2, StringSplitOptions.RemoveEmptyEntries))
.Select(parts => (start: parts[0], end: parts[1]))
.ToListAsync();
var startPoints = connections.Select(connection => connection.start).ToHashSet();
var unconnectedEndpoints = connections.Select(connection => connection.end)
.Where(endpoint => !startPoints.Contains(endpoint))
.ToHashSet();
foreach (var endpoint in unconnectedEndpoints.Order())
Console.WriteLine(endpoint);
}
private static async IAsyncEnumerable<string> ReadLinesAsync(this TextReader reader)
{
while (await reader.ReadLineAsync() is { } line)
yield return line;
}
}
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