\ SEND+MORE=MONEY program by M. Anton Ertl 2023

create occupationmap 10 allot
\ each entry is 0 if free, non-0 if occupied

: occupation! ( f u -- )
    occupationmap + c! ;

: occupy< ( u -- u )
    ]] dup >r occupationmap + c@ 0= if true r@ occupation! r@ [[ ; immediate

: >occupy ( -- )
    ]] false r@ occupation! then rdrop [[ ; immediate

: try< ( run-time: -- u )
    ]] 10 0 do i occupy< [[ ; immediate

: >try ( run-time: -- )
    ]] >occupy loop [[ ; immediate


: .solution {: s e n d m o r y -- :}
  s 0 .r e 0 .r n 0 .r d 0 .r ." +"
  m 0 .r o 0 .r r 0 .r e 0 .r ." ="
  m 0 .r o 0 .r n 0 .r e 0 .r y 0 .r ;

: smm ( -- )
 \ SEND+MORE=MONEY
 occupationmap 10 erase
 try< {: s :} s 0 > if
  try< {: m :} m 0 > if
   try< {: e :}
    try< {: d :}
     try< {: n :}
      try< {: o :}
       try< {: r :}
        try< {: y :}
         s 1000 * e 100 * + n 10 * + d + {: send :}
         m 1000 * o 100 * + r 10 * + e + {: more :}
         m 10000 * o 1000 * + n 100 * + e 10 * + y + {: money :}
         send more + money = if
          cr s e n d m o r y .solution
         then
        >try
       >try
      >try
     >try
    >try
   >try
  then >try
 then >try ;