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#include <string>
#include <vector>
#include <utility>
#include <iostream>
std::string flip( const std::string & doorstate ) {
if ( doorstate == "open" ) {
return "closed" ;
}
else {
return "open" ;
}
}
int main( ) {
std::vector<std::pair<std::string, int> > theDoors ;
for ( int i = 1 ; i < 501 ; i++ ) {
theDoors.push_back( std::make_pair( "open" , i ) ) ;
}
for ( int i = 2 ; i < 501 ; i++ ) {
if ( i < 251 ) {
for ( int j = i ; j < 501 ; j += i ) {
const std::string state {theDoors[ j - 1].first } ;
std::string newState { flip ( state ) } ;
theDoors[ j - 1 ] = std::make_pair( newState , theDoors[ j - 1 ].second ) ;
}
}
else {
theDoors[ i - 1 ] = std::make_pair( flip( theDoors[ i - 1 ].first ) ,
theDoors[ i - 1 ].second ) ;
}
}
for ( auto & p : theDoors ) {
if ( p.first == "open" ) {
std::cout << "Door " << p.second << " is open!\n" ;
}
}
return 0 ;
}
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