ABCDEFGPPP.cs

using System;
using System.Linq;

public class Program {
	public static void Main() {
		for (int i = 10; i < 100; i++) {
			if (CountDigits(i, 111 - i) == 4) {
				for (int j = 10; j < 100; j++) {
					if (CountDigits(j, i + j, i, 111 - i) == 8 && i + j > 9 && i + j < 100) {			
						Console.WriteLine(string.Format("{2} - {3} = {0} + {1} = 111", i, 111 - i, j, i + j));
					}
				}
			}
		}
	}
	
	public static int CountDigits(params int[] numbers) {
		return numbers.SelectMany(o => new int[]{o / 10, o % 10}).Distinct().Count();
		/*
		var x = new HashSet<int>();
		foreach (var n in numbers) {
			x.Add(n / 10);
			x.Add(n % 10);
		}
		return x.Count;
		*/
	}
	
}