small update and setup git on new devices

Author: Mrezadwiprasetiawan

.gitignore

@@ -9,6 +9,9 @@ compile_commands.json
 
 #swap file from vim
 **/*.sw*
+<<<<<<< HEAD
 
 #vscode file
 .vscode
+=======
+>>>>>>> refs/remotes/origin/main

discrete/include/derangement.hxx

@@ -1,5 +1,6 @@
 #include <cstdint>
 #include <type_traits>
+<<<<<<< HEAD
 #include <vector>
 
 namespace Discrete {
@@ -26,4 +27,14 @@ public:
 
   }
 };
-} // namespace Discrete
+} // namespace Discrete
+=======
+
+template <typename T, typename Ret = uint64_t>
+std::enable_if_t<std::is_arithmetic_v<T>, Ret>
+derangement(T n){
+  if (!n) return 1;
+  if (n==1) return 0;
+  return (n-1)*(derangement(n-1)+derangement(n-2));
+}
+>>>>>>> refs/remotes/origin/main

discrete/include/factorial.hxx

@@ -0,0 +1,13 @@
+#pragma once
+#include <type_traits>
+
+template <typename T>
+std::enable_if_t<std::is_arithmetic_v<T>> factorial(T n) {
+  if (n == 1) return 1;
+  return n * factorial(n - 1);
+}
+
+template <typename T>
+T permutation(T n){
+  return factorial<T>(n);
+}