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CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

public static class Extensions {
	public static KeyValuePair<K, V> After<K, V>( this Dictionary<K, V> dictionary, K key ) {
		Int32 position = dictionary.Keys.ToList().IndexOf( key );
		
		if( position == -1 )
			throw new ArgumentException( "No match.", "key" );
		
		position++;
		
		if( position >= dictionary.Count )
			position = 0;
		
		K k = dictionary.Keys.ToList()[ position ];
		V v = dictionary.Values.ToList()[ position ];
		
		return new KeyValuePair<K, V>( k, v );
	}
	public static KeyValuePair<K, V> After<K, V>( this Dictionary<K, V> dictionary, V value ) {
		Int32 position = dictionary.Values.ToList().IndexOf( value );
		
		if( position == -1 )
			throw new ArgumentException( "No match.", "value" );
		
		position++;
		
		if( position >= dictionary.Count )
			position = 0;
		
		K k = dictionary.Keys.ToList()[ position ];
		V v = dictionary.Values.ToList()[ position ];
		
		return new KeyValuePair<K, V>( k, v );
	}
	public static KeyValuePair<K, V> Before<K, V>( this Dictionary<K, V> dictionary, K key ) {
		Int32 position = dictionary.Keys.ToList().IndexOf( key );
		
		if( position == -1 )
			throw new ArgumentException( "No match.", "key" );
		
		position--;
		
		if( position < 0 )
			position = dictionary.Count - 1;
		
		K k = dictionary.Keys.ToList()[ position ];
		V v = dictionary.Values.ToList()[ position ];
		
		return new KeyValuePair<K, V>( k, v );
	}
	public static KeyValuePair<K, V> Before<K, V>( this Dictionary<K, V> dictionary, V value ) {
		Int32 position = dictionary.Values.ToList().IndexOf( value );
		
		if( position == -1 )
			throw new ArgumentException( "No match.", "value" );
		
		position--;
		
		if( position < 0 )
			position = dictionary.Count - 1;
		
		K k = dictionary.Keys.ToList()[ position ];
		V v = dictionary.Values.ToList()[ position ];
		
		return new KeyValuePair<K, V>( k, v );
	}
}					
public class Program
{
	public static void Main()
	{
		Dictionary<String, Int64>
			dictionary = new Dictionary<String, Int64>() {
				{ "1000L", 1000L },
				{ "2000L", 2000L },
				{ "3000L", 3000L },
				{ "4000L", 4000L },
				{ "5000L", 5000L },
				{ "6000L", 6000L },
			};
		
		Random
			random = new Random();
		
		while( true ) {
			Int64
				value = random.Next( 1, 7 ) * 1000L;
			Int32
				position = dictionary.Values.ToList().IndexOf( value );
			String
				key = dictionary.Keys.ToList()[ position ];
			
			KeyValuePair<String, Int64>
				after = dictionary.After( value ),
			before = dictionary.Before( value );
			
			Console.WriteLine( "Value: " + value );
			Console.WriteLine( "Key: " + key );
			
			Console.WriteLine();
			
			Console.WriteLine( "Next Value: " + after.Value );
			Console.WriteLine( "Next Key: " + after.Key );
			
			Console.WriteLine();
			
			Console.WriteLine( "Previous Value: " + before.Value );
			Console.WriteLine( "Previous Key: " + before.Key );
			
			Console.ReadLine();
			
			Console.Clear();
		}
	}
}