add week 1

4 files changed, 94 insertions, 0 deletions

diff --git a/week1/Collatz.cs b/week1/Collatz.cs
new file mode 100644
index 0000000..556a4c4
--- /dev/null
+++ b/week1/Collatz.cs
@@ -0,0 +1,25 @@
+namespace ALGA {
+	public class Collatz {
+		public static int collatz_recursive(int n) {
+			if (n <= 0) return -1;
+			if (n == 1) return 0;
+			if (n % 2 == 0) n /= 2;
+			else n = n * 3 + 1;
+			return 1 + collatz_recursive(n);
+		}
+
+		public static int collatz_iterative(int n) {
+			if (n <= 0) return -1;
+			if (n == 1) return 0;
+
+			int steps = 0;
+			while (n != 1) {
+				if (n % 2 == 0) n /= 2;
+				else n = n * 3 + 1;
+				steps++;
+			}
+			return steps;
+		}
+	}
+}
+
diff --git a/week1/Fibonacci.cs b/week1/Fibonacci.cs
new file mode 100644
index 0000000..f5d7a4d
--- /dev/null
+++ b/week1/Fibonacci.cs
@@ -0,0 +1,28 @@
+namespace ALGA {
+	public class Fibonacci {
+		public static int fibonacci_recursive(int n) {
+			if (n <= 0) return 0;
+			if (n == 1) return 1;
+			return fibonacci_recursive(n - 1) + fibonacci_recursive(n - 2);
+		}
+
+		public static int fibonacci_iterative(int n) {
+			if (n < 0) return 0;
+			int a = 0, b = 1;
+			for (int i = 0; i < n; i++)
+				(a, b) = (b, a + b);
+			return a;
+		}
+
+		public enum Answer { IterativeIsFaster, RecursiveIsFaster };
+
+		public static Answer which_is_faster() {
+			/**
+			 * Iterative is 'sneller' omdat deze O(n) is in tegenstelling tot de
+			 * recursieve versie die O(2^n) is
+			 */
+			return Answer.IterativeIsFaster;
+		}
+	}
+}
+
diff --git a/week1/PyramidProblem.cs b/week1/PyramidProblem.cs
new file mode 100644
index 0000000..1be67d9
--- /dev/null
+++ b/week1/PyramidProblem.cs
@@ -0,0 +1,22 @@
+namespace ALGA {
+	public class PyramidProblem {
+		public static int triangular_number_recursive(int n) {
+			if (n <= 0) return 0;
+			return n + triangular_number_recursive(n - 1);
+		}
+
+		public static int triangular_number_iterative(int n) {
+			if (n <= 0) return 0;
+			int total = 0;
+			for (int i = 1; i <= n; i++)
+				total += i;
+			return total;
+		}
+
+		public static int triangular_number_function(int n) {
+			if (n <= 0) return 0;
+			return (n + 1) * n / 2;
+		}
+	}
+}
+
diff --git a/week1/StringReverse.cs b/week1/StringReverse.cs
new file mode 100644
index 0000000..2d09b0f
--- /dev/null
+++ b/week1/StringReverse.cs
@@ -0,0 +1,19 @@
+using System;
+
+namespace ALGA {
+	public class StringReverse {
+		public static String string_reverse(String s) {
+			if (s.Length == 0) return s;
+			return s[s.Length - 1] + string_reverse(s.Substring(0, s.Length - 1));
+		}
+
+		public static bool is_palindrome(String s) {
+			for (int front = 0; front < s.Length; front++) {
+				int back = s.Length - 1 - front;
+				if (s[front] != s[back]) return false;
+			}
+			return true;
+		}
+	}
+}
+