- Added solutions by Ulrich Rieke.

1 files changed, 67 insertions, 0 deletions

diff --git a/challenge-055/ulrich-rieke/cpp/ch-2.cpp b/challenge-055/ulrich-rieke/cpp/ch-2.cpp
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+++ b/challenge-055/ulrich-rieke/cpp/ch-2.cpp
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+#include <iostream>
+#include <vector>
+#include <iterator>
+#include <algorithm>
+#include <utility>
+#include <cstdlib>
+
+//this function creates pairs of neighbouring numbers in a vector
+std::vector<std::pair<int, int>> createDoublets ( const std::vector<int> & numbers ) {
+  std::vector<std::pair<int , int>> doublets ;
+  int len = numbers.size( ) ;
+  for ( int i = 0 ; i < len - 1 ; i++ ) {
+      std::pair<int , int> p { *(numbers.begin( ) + i ) ,
+        *(numbers.begin( ) + i + 1 ) } ;
+      doublets.push_back( p ) ;
+  }
+  return doublets ;
+}
+
+//in order to create a "wavy list of numbers", a vector of numbers is
+//converted into a vector of pairs of neighbouring numbers. To be wavy,
+//even-indexed pairs must be descending, odd-indexed ones must ascend.
+//if this holds true for all pairs a permutation is "wavy"
+bool myCondition( const std::vector<int> & numbers ) {
+  std::vector<std::pair<int, int>> doublets { createDoublets( numbers ) } ;
+  int len = doublets.size( ) ;
+  std::vector<bool> validWavy ;
+  for (int i = 0 ; i < len ; i++ ) {
+      std::pair<int , int> p = doublets[ i ] ;
+      validWavy.push_back (( i % 2 == 0 ) && ( p.first >= p.second ) ) ;
+      validWavy.push_back (( i % 2 == 1 ) && ( p.first <= p.second ) ) ;
+  }
+  int i = 0 ;
+  for ( auto b : validWavy ) {
+      if ( b )
+    i++ ;
+  }
+  return ( i == len ) ;
+}
+
+//numbers are entered as arguments on the command line. A minimum number
+//of 2 is desirable and requested
+int main( int argc, char * argv[] ) {
+  std::vector<int> input ;
+  if ( argc < 3 ) {
+      std::cout << "There is little sense in permuting such short sequences!\n" ;
+      return 1 ;
+  }
+  for ( int i = 1 ; i < argc ; i++ ) {
+      input.push_back( std::atoi( argv[ i ] ) ) ;
+  }
+  std::vector<std::vector<int>> permus ;
+  std::vector<std::vector<int>> wavies ;
+  do {
+      permus.push_back( input ) ;
+  } while ( std::next_permutation( input.begin( ) , input.end( ) )) ;
+  std::copy_if( permus.begin( ) , permus.end( ) ,
+    std::back_inserter( wavies ) , myCondition ) ;
+  for ( auto & it : wavies ) {
+      std::cout << "[ " ;
+      for ( int i : it ) {
+    std::cout << i << " " ;
+      }
+      std::cout << " ]\n" ;
+  }
+  return 0 ;
+}