ProjectEuler_1to5.cs

// ProjectEuler_1to5.cs
// Joe Mortillaro
// 10/1/2014

using System.Collections.Generic; // This allows Lists to be used.
using System;
using System.Linq;  

public class ProjectEuler_1to5
{
   public static void Main() 
   {
        var problem01 = new Problem01();
        System.Console.WriteLine("Answer 01: " + problem01.Solve());

        var problem02 = new Problem02();
        System.Console.WriteLine("Answer 02: " + problem02.GetAnswer());
        
        var problem03 = new Problem03();
        System.Console.WriteLine("Answer 03: " + problem03.AnswerNumber);
        
        var problem04 = new Problem04();
        System.Console.WriteLine("Answer 04: " + problem04.getAnswer());
        
        var problem05 = new Problem05();
        System.Console.WriteLine("Answer 05: " + problem05.getAnswer());
    }
}

public static class Tools 
{
    static public List<long> Factor(long number) 
    {
        long x = 2;
        long y = number;
        var returnList = new List<long>();
        do 
        {
            if (y % x == 0) 
            {
                returnList.Add(x);
                y = y/x;
                x = 2;
            }
        } while (++x <= y/2);
 
        if (y != 1) returnList.Add(y);
        return returnList;
    }
    
    static public Dictionary<long, long> GetCount(List<long> numberList) 
    {
        var returnDict = new Dictionary<long, long>();
        foreach (long x in numberList) 
        {
            if (returnDict.ContainsKey(x) == true) 
            {
                returnDict[x] += 1;
            }
            else if (returnDict.ContainsKey(x) == false) {
                returnDict.Add(x, 1);
            }
        }
        return returnDict;
    }
}

// Problem 1:
// If we list all the natural numbers below 10 that are multiples of 
// 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23. 
// Find the sum of all the multiples of 3 or 5 below 1000. 
// Answer: 233168 
class Problem01 
{
    public int Solve() 
    {
        var answerNumber = 0;
        for (var x = 1; x < 1000; ++x) 
        {
            if  (x % 3 == 0 || x % 5 == 0) 
            {
                answerNumber += x;
            }
        }
        return answerNumber;
    }
}

// Problem 2: 
// Each new term in the Fibonacci sequence is generated by adding the 
// previous two terms. By starting with 1 and 2, the first 10 terms 
// will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... 
// By considering the terms in the Fibonacci sequence whose values do 
// not exceed four million, find the sum of the even-valued terms.
// Answer: 4613732
class Problem02 
{
    int answerNumber = 0;
    public int GetAnswer() 
    {
        return answerNumber;
    }
    public Problem02() 
    {
        answerNumber = 0;
        var fibList = new List<int>();
        var x = 0;
        var y = 1;
        var z = 1;
        while (z < 4000000) 
        {
            z = x + y;
            x = y;
            y = z;
            if (z % 2 == 0) fibList.Add(z);
        }
        answerNumber = fibList.Sum();
    }
}

// Problem 3:
// The prime factors of 13195 are 5, 7, 13 and 29.
// What is the largest prime factor of the number 600851475143 ?
// Answer: 6857
class Problem03 
{
    public long AnswerNumber { get; set;}   
    public Problem03() 
    {
        AnswerNumber = 0;
        var factorList = new List<long>();
        factorList = Tools.Factor(600851475143);
        long z = 1;
        
        foreach (long x in factorList) 
        {
            z = z * x;
            if (x > AnswerNumber) 
            {
                AnswerNumber = x;
            }
        }
    }
}

// Problem 4:
// A palindromic number reads the same both ways. The largest 
// palindrome made from the product of two 2-digit numbers is 
// 9009 = 91(99).
// Find the largest palindrome made from the product of two 3-digit 
// numbers.
// Answer: 906609
class Problem04 
{
    long answerNumber = 0;

    bool test(long n) 
    {
        var returnValue = true;
        string s = n.ToString();
        for (int x = 0; x <= s.Length/2; ++x) 
        {
            if (s[x] != s[s.Length - x-1]) 
            {
                returnValue = false;
            }
        }
        return returnValue;      
    }

    public Problem04() {
        for (int y = 999; y > 0; --y) 
        {
            for (int x = y-1; x > 0; --x) 
            {
                if (x*y <= this.answerNumber) break;
                if (this.test(x*y) == true) 
                {
                    this.answerNumber = x*y;
                }
            }
            if (y*(y-1) <= this.answerNumber) break;
        }
    }
    
    public int getAnswer() 
    {
        return (int)answerNumber;
    }
}

// Problem 5:
// 2520 is the smallest number that can be divided by each of the 
// numbers from 1 to 10 without any remainder.
// What is the smallest positive number that is evenly divisible 
// by all of the numbers from 1 to 20?
// Answer: 232792560
class Problem05 
{
    long answerNumber = 1;
    
    public Problem05() 
    {
        var factorCount = new Dictionary<long, long>();
        for (int x = 1; x <= 20; ++x) 
        {
            var tempCount = Tools.GetCount(Tools.Factor(x));
            foreach (long i in tempCount.Keys) 
            {
                if (factorCount.ContainsKey(i)) 
                {
                    if (factorCount[i] < tempCount[i]) 
                    {
                        factorCount[i] = tempCount[i];
                    }
                }
                else 
                {
                    factorCount.Add(i, tempCount[i]);
                }
            }            
        }
        foreach (long i in factorCount.Keys) 
        {
            answerNumber *= (long) Math.Pow(i, factorCount[i]);
        }
    }
    
    public int getAnswer() 
    {
        return (int) answerNumber;
    }
}