using System;
using System.Collections.Generic;
 
public class Test
{
        public static void Main()
        {
           var c = new Counter<int>();
           c.Increment(1);
           c.Increment(2);
           c.Increment(1);
           c.Increment(1);
           foreach (var kvp in c) {
               Console.WriteLine(kvp);
           }
        }
        public class Counter<T> : IEnumerable<KeyValuePair<T, int>> {
        private Dictionary<T, int> counts = new Dictionary<T, int>();
 
        public void Increment(T key) {
            int current;
            bool exists = counts.TryGetValue(key, out current);
            if (exists) {
                counts[key]++;
            }
            else {
                counts[key] = 1;
            }
        }
 
        IEnumerator<KeyValuePair<T, int>>
            IEnumerable<KeyValuePair<T, int>>.GetEnumerator() {
            return ((IEnumerable<KeyValuePair<T, int>>) counts).GetEnumerator();
        }
 
        System.Collections.IEnumerator
            System.Collections.IEnumerable.GetEnumerator() {
            return counts.GetEnumerator();
        }
    }
}