# C#: Project Euler Solutions to Problems 9, 13, and 38

For solving ten consecutive problems (1-10).

http://projecteuler.net/problem=9

a2 + b2 = c2

There exists exactly one Pythagorean triplet for which a + b + c = 1000.
Find the product abc.

```for (int a = 1; a < 1000; a++) { for (int b = 1; b < 1000; b++) { double a_pow2 = Math.Pow(a, 2); double b_pow2 = Math.Pow(b, 2); double c_root = Math.Sqrt(a_pow2 + b_pow2); if ((a + b + c_root) == 1000.00) { Console.WriteLine("a "+a+" b "+b+" c "+c_root+" product : "+(a * b * c_root)); break; } } }```

http://projecteuler.net/problem=13

Work out the first ten digits of the sum of the following one-hundred 50-digit numbers.

```string[] linerows = totalstring.Split('\n'); long sum = 0; foreach (string row in linerows) { // Console.WriteLine(row); string longnum = row; string num11 = longnum.Substring(0, 11); long num = long.Parse(num11); sum += num; } Console.WriteLine(sum.ToString().Substring(0, 10));```

http://projecteuler.net/problem=38

What is the largest 1 to 9 pandigital 9-digit number that can be formed as the concatenated product of an integer with (1,2, … , n) where n 1?

```static void Main(string[] args) { int number = 0; int numberofappend = 2; int max = 0; while (true) { number++; string catstring = appendmore(number, numberofappend); if (catstring.Length > 9) { number = 0; numberofappend++; } else if (catstring.Length == 9 && Order(catstring)) { int catint = int.Parse(catstring); if (max < catint) { max = catint; Console.WriteLine("max so far : "+ max); } } } } public static string appendmore(int num, int howmany) { string cat = ""; for (int i = 1; i <= howmany; i++) cat += "" + num * i; return cat; } public static bool Order(string n) { string mynum = "" + n; int[] int_array = new int[mynum.Length]; for (int i = 0; i < mynum.Length; i++) { int_array[i] = int.Parse(mynum[i].ToString()); } Array.Sort(int_array); if (int_array[0] == 1) { int count = 2; for (int j = 1; j < int_array.Length; j++) { if (count == int_array[j]) count++; else return false; } } else return false; return true; }```