- Added solutions by Ulrich Rieke.

1 files changed, 55 insertions, 0 deletions

diff --git a/challenge-175/ulrich-rieke/cpp/ch-2.cpp b/challenge-175/ulrich-rieke/cpp/ch-2.cpp
new file mode 100644
index 0000000000..2f910a3bfc
--- /dev/null
+++ b/challenge-175/ulrich-rieke/cpp/ch-2.cpp
@@ -0,0 +1,55 @@
+#include <iostream>
+#include <vector>
+#include <numeric>
+#include <algorithm>
+
+int my_gcd( int a , int b ) { //Euclid's algorithm
+  if ( b >= a )
+      std::swap( a , b ) ;
+  while ( a != b ) {
+      a = a - b ;
+      if ( b >= a )
+    std::swap( a , b ) ;
+  }
+  return a ;
+}
+
+int myPhi(  int n ) {
+  std::vector<int> totatives ;
+  for ( int i = 1 ; i < n ; i++ ) {
+      if ( my_gcd( i , n ) == 1 )
+    totatives.push_back( i ) ;
+  }
+  return totatives.size( ) ;
+}
+
+bool isPerfectTotient( int n ) {
+  if ( n == 1 ) {
+      return false ;
+  }
+  int current = n ;
+  std::vector<int> totients ;
+  do {
+      current = myPhi( current ) ;
+      totients.push_back( current ) ;
+  } while ( current != 1 ) ;
+  return std::accumulate( totients.begin( ) , totients.end( ) , 0 ) == n ;
+}
+
+int main( ) {
+  std::vector<int> perfectTotients ;
+  int current = 1 ;
+  while ( perfectTotients.size( ) != 20 ) {
+      if ( isPerfectTotient( current ) ) {
+    perfectTotients.push_back( current ) ;
+      }
+      current++ ;
+  }
+  for ( int i : perfectTotients ) {
+      std::cout << i ;
+      if ( i != perfectTotients.back( ) )
+    std::cout << ',' ;
+  }
+  std::cout << std::endl ;
+  return 0 ;
+}