public:

using value_type = typename std::iterator_traits<iterator>::value_type ;

using reference = typename std::iterator_traits<iterator>::reference ;

using pointer = typename std::iterator_traits<iterator>::pointer ;

StrideIterator( iterator it_, int n_ ) : it(it_), n(n_){}

StrideIterator& operator++(){

it += n ;

return *this ;

}

StrideIterator operator++(int){

StrideIterator orig(it,n) ;

it += n ;

return orig ;

}

StrideIterator& operator--(){

it -= n ;

return *this ;

}

StrideIterator operator--(int){

StrideIterator orig(it,n) ;

it -= n ;

return orig ;

}

StrideIterator operator+( int m ) const {

return StrideIterator( it + m*n, n );

}

StrideIterator operator-( int m ) const {

return StrideIterator( it - m*n, n );

}

StrideIterator& operator+=( int m ){

it += n*m ;

return *this ;

}

StrideIterator& operator-=( int m ){

it -= n*m ;

return *this ;

}

int operator-( const StrideIterator& other){

return (other.it - it) / n ;

}

bool operator==( const StrideIterator& other) { return it == other.it ; }

bool operator!=( const StrideIterator& other) { return it != other.it ; }

bool operator<( const StrideIterator& other ) { return it < other.it ; }

bool operator>( const StrideIterator& other ) { return it > other.it ; }

bool operator<=( const StrideIterator& other ) { return it <= other.it ; }

bool operator>=( const StrideIterator& other ) { return it >= other.it ; }

inline reference operator[](int i){

return it[i*n] ;

}

inline reference operator*() {

return *it ;

}

private:

iterator it ;

int n ;