DB<73> $_=$r; s/(#\S+\s?)\K(.+\1)(?{say "$_ ($1) - ($2) pos:",pos($_)})//g ;say                                             
#1 #2 #3 #1 #3 #2 #3 #2 (#1 ) - (#2 #3 #1 ) pos:13                                                                           
#1 #2 #3 #1 #3 #2 #3 #2 (#3 ) - (#2 #3 ) pos:22                                                                              
#1 #3 #2