Increment the value of { num , den } in the map
if ( mp . has ( ` ${ num } ${ den } ` ) ) { mp . set ( ` ${ num } ${ den } ` , mp . get ( ` ${ num } ${ den } ` ) + 1 ) } else { mp . set ( ` ${ num } ${ den } ` , 1 ) }