1 files changed, 38 insertions, 0 deletions
diff --git a/challenge-236/ulrich-rieke/cpp/ch-2.cpp b/challenge-236/ulrich-rieke/cpp/ch-2.cpp
new file mode 100755
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+++ b/challenge-236/ulrich-rieke/cpp/ch-2.cpp
@@ -0,0 +1,38 @@
+#include <iostream>
+#include <vector>
+#include <numeric>
+#include <set>
+#include <algorithm>
+
+//my assumption is that you can always find a loop if the starting array 
+//is a random shuffle of all the indices of a vector from 0 to len - 1 where
+//len is the length of the array. 
+
+int main( ) {
+   std::vector<int> numbers( 20 ) ;
+   std::iota( numbers.begin( ) , numbers.end( ) , 1 ) ;
+   std::random_shuffle( numbers.begin( ) , numbers.end( ) ) ;
+   int loops = 0 ;
+   for ( int pos = 0 ; pos < 20 ; pos++ ) {
+      if ( numbers[ pos ] == pos ) { 
+	 loops++ ;
+      }
+      else {
+	 std::set<int> already_seen ;
+	 int num = numbers[ pos ] ;
+	 auto p = already_seen.insert( num ) ;
+	 while ( p.second ) {
+	    if ( already_seen.find( num ) != already_seen.end( ) ) {
+	       loops++ ;
+	       break ;
+	    }
+	    else {
+	       num = numbers[ num ] ;
+	       p = already_seen.insert( num ) ;
+	    }
+	 }
+      }
+   }
+   std::cout << loops << std::endl ;
+   return 0 ;
+}