Merge remote-tracking branch 'upstream/master'

1 files changed, 46 insertions, 0 deletions

diff --git a/challenge-147/ulrich-rieke/cpp/ch-1.cpp b/challenge-147/ulrich-rieke/cpp/ch-1.cpp
new file mode 100644
index 0000000000..975ba98215
--- /dev/null
+++ b/challenge-147/ulrich-rieke/cpp/ch-1.cpp
@@ -0,0 +1,46 @@
+#include <iostream>
+#include <string>
+#include <cmath>
+#include <vector>
+
+bool isPrime( int n ) {
+  if ( n == 1 )
+      return false ;
+  if ( n == 2 )
+      return true ;
+  int root = static_cast<int>( floor( sqrt( static_cast<double>( n ) ))) ;
+  for ( int i = 2 ; i < root + 1 ; i++ )
+      if ( n % i == 0 )
+    return false ;
+  return true ;
+}
+
+bool isLeftTruncatablePrime( int n ) {
+  if ( ! isPrime( n ) )
+      return false ;
+  std::string numberstring( std::to_string( n ) ) ;
+  auto found = numberstring.find( '0' ) ;
+  if ( found != std::string::npos )
+      return false ;
+  int len = static_cast<int>(numberstring.length( ) ) ;
+  for ( int i = 0 ; i < len ; i++ ) {
+      int num = std::stoi( numberstring.substr( i ) ) ;
+      if ( ! isPrime( num ) )
+    return false ;
+  }
+  return true ;
+}
+
+int main( ) {
+  std::vector<int> leftTruncatables ;
+  int current = 0 ;
+  while ( leftTruncatables.size( ) < 20 ) {
+      current++ ;
+      if ( isLeftTruncatablePrime( current ) )
+    leftTruncatables.push_back( current ) ;
+  }
+  for ( int i : leftTruncatables )
+      std::cout << i << ' ' ;
+  std::cout << std::endl ;
+  return 0 ;
+}