- Added solutions by Ulrich Rieke.

1 files changed, 66 insertions, 0 deletions

diff --git a/challenge-169/ulrich-rieke/cpp/ch-2.cpp b/challenge-169/ulrich-rieke/cpp/ch-2.cpp
new file mode 100644
index 0000000000..ffbcfcdd34
--- /dev/null
+++ b/challenge-169/ulrich-rieke/cpp/ch-2.cpp
@@ -0,0 +1,66 @@
+#include <iostream>
+#include <algorithm>
+#include <map>
+#include <vector>
+#include <numeric>
+#include <iterator>
+
+std::vector<int> primeDecompose( int n ) {
+  std::vector<int> primeFactors ;
+  int current = 2 ;
+  while ( n != 1 ) {
+      if ( n % current == 0 ) {
+    primeFactors.push_back( current ) ;
+    n /= current ;
+      }
+      else {
+    current++ ;
+      }
+  }
+  return primeFactors ;
+}
+
+int my_gcd( int a , int b ) {
+  std::vector<int> firstFactors( primeDecompose( a ) ) ;
+  std::vector<int> secondFactors( primeDecompose( b ) ) ;
+  std::vector<int> common ;
+  std::set_intersection( firstFactors.begin( ) , firstFactors.end( ) ,
+    secondFactors.begin( ) , secondFactors.end( ) ,
+    std::inserter( common, common.begin( ) )) ;
+  return std::accumulate( common.begin( ) , common.end( ) , 1 ,
+    std::multiplies( ) ) ;
+}
+
+bool isAchilles( int n ) {
+  std::vector<int> primeFactors( primeDecompose( n ) ) ;
+  std::map<int , int> factorCount ;
+  for ( int i : primeFactors ) {
+      factorCount[ i ]++ ;
+  }
+  std::vector<int> exponents ;
+  for ( auto it = factorCount.begin( ) ; it != factorCount.end( ) ; ++it ) {
+      exponents.push_back( it->second ) ;
+  }
+  if ( *std::min_element(exponents.begin( ) , exponents.end( ) ) >= 2 ) {
+      int start = *exponents.begin( ) ;
+      return (std::accumulate( exponents.begin( ) , exponents.end( ) , start ,
+        []( int a , int b ){ return my_gcd( a , b ) ; } ) == 1 ) ;
+  }
+  else
+      return false ;
+}
+
+int main( ) {
+  std::vector<int> achillesNumbers ;
+  int current = 2 ;
+  while ( achillesNumbers.size( ) != 20 ) {
+      if ( isAchilles( current ) ) {
+    achillesNumbers.push_back( current ) ;
+      }
+      current++ ;
+  }
+  for ( int i : achillesNumbers )
+      std::cout << i << " " ;
+  std::cout << std::endl ;
+  return 0 ;
+}