C# solution for 'Store Credit' from code jam 2010

IOExtensions.cs

/*
 * Created by SharpDevelop.
 * Date: 5/25/2013
 * Time: 3:30 PM
 * 
 */
using System;
using System.IO;
using System.Collections.Generic;

namespace Utility
{
  /// <summary>
	/// Extension methods to make IO easier
	/// </summary>
	public static class IOExtensions
	{
		/// <summary>
		/// Read an int (assumes the entire line contains a single integer)
		/// </summary>
		public static Int32 ReadInt(this StreamReader readerObj)
		{
			return Convert.ToInt32(readerObj.ReadLine());
		}
		
		/// <summary>
		/// Read a line with an array of integers (assumes that are separated by spaces)
		/// </summary>
		public static List<Int32> ReadIntList(this StreamReader readerObj)
		{
			List<Int32> intList = new List<Int32>();
			
			String[] inputNums = (readerObj.ReadLine()).Split(' ');
			
			foreach (string singleNum in inputNums) 
			{
				intList.Add(Convert.ToInt32(singleNum));
			}
			
			return intList;
		}
	}
}

Program.cs

/*
 * Created by SharpDevelop.
 * Date: 5/25/2013
 * Time: 3:06 PM
 * 
 * Problem description: https://code.google.com/codejam/contest/351101/dashboard
 */
using System;
using System.Collections.Generic;
using System.IO;

using Utility;

namespace StoreCredit
{
  class Program
	{		
		public static void Main(string[] args)
		{
			Console.WriteLine("Please enter input file name:");
			String inputFileName = Console.ReadLine();
						
			Console.WriteLine("Please enter output file name:");
			String outputFileName = Console.ReadLine();
			
			StreamReader fileReader = new StreamReader(inputFileName);
			
			StreamWriter fileWriter = new StreamWriter(outputFileName);
			
			//The first line of input gives the number of cases
			int N = fileReader.ReadInt();
			
			//Run through the cases one by one
			int credit;
			int numItems;
			List<int> items;
			
			for(int i = 0; i < N; i++)
			{
				credit = fileReader.ReadInt();
				numItems = fileReader.ReadInt();
				
				items = fileReader.ReadIntList();
				
				fileWriter.WriteLine("Case #{0}: {1}", i+1, FindItems(items, credit));
			}
			
			fileReader.Close();
			fileWriter.Close();
						
			Console.ReadKey(true);
		}

		/// <summary>
		/// Returns a string "A B" where A and B are the two indices whose
		/// price adds up the store credit
		/// </summary>
		/// <param name="items"></param>
		/// <param name="credit"></param>
		/// <returns></returns>
		private static string FindItems(List<Int32> items, int credit)
		{
			//Create a boolean array of size 'credit' since we can safely ignore 
			//items that cost more than the credit we have
			int[] itemCosts = new int[credit];
			
			int currentItem;
			for (int i = 0; i < items.Count; i++) 
			{
				currentItem = items[i];
				
				if(currentItem < credit)
				{
					//Find the amount required in order to fill credit with current item
					//and another item
					if(itemCosts[credit - currentItem] != 0)
					{						
						return String.Format("{0} {1}", itemCosts[credit - currentItem], i+1);
					}
					else
					{
						itemCosts[currentItem] = i + 1;
					}
				}
			}
			
			return "";
		}		
	}
}