Days 1-3

advent-2021-01a.fs

+variable last
+: read-num ( -- n n? ) 0 0   pad   pad 10 accept   >number   nip nip not ;
+: ?deeper ( n -- f ) dup   last @ >   swap last ! ;
+: get-first-depth ( -- ) read-num drop last ! ;
+: count-deepers ( n -- ) begin read-num while ?deeper if 1+ then repeat drop ;
+get-first-depth 0 count-deepers ." Answer:" .
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advent-2021-01b.fs

+: addrs ( a -- a a' a'' ) dup cell + dup cell + ;
+: slide ( a -- n' ) addrs  dup @ >r  over @ swap !  swap @ swap !  r> ;
+: mkwindow
+  create ( -- ) 0 , 0 , 0 ,
+  does> ( n [a] -- ?deeper ) dup >r   slide swap dup r> !   < ;
+
+mkwindow >w>
+
+: read-num ( -- n n? ) 0 0   pad   pad 10 accept   >number   nip nip not ;
+: first-window ( -- ) 3 0 do read-num drop >w> drop loop ;
+: count-deepers ( n -- n ) begin read-num while >w> if 1+ then repeat drop ;
+first-window 0 count-deepers ." Answer:" .
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advent-2021-02a.fs

+: get-n ( -- n ) 0 0   bl parse   >number 2drop drop ;
+variable horiz 0 horiz !
+variable depth 0 depth !
+: forward ( "N" -- ) get-n horiz +! ;
+: up ( "N" -- ) get-n negate depth +! ;
+: down ( "N" -- ) get-n depth +! ;
+: report ( -- ) horiz @ depth @ * ;
+
+\ Then, paste your input into the repl and type "report".
+\ Data is code.
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advent-2021-02b.fs

+: get-n ( -- n ) 0 0   bl parse   >number 2drop drop ;
+variable horiz 0 horiz !
+variable depth 0 depth !
+variable aim 0 aim !
+: forward ( "N" -- ) get-n dup horiz +! aim @ * depth +! ;
+: up ( "N" -- ) get-n negate aim +! ;
+: down ( "N" -- ) get-n aim +! ;
+: report ( -- ) horiz @ depth @ * ;
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advent-2021-03a.fs

+variable n 0 n !
+variable bit 0 bit !
+: pops ( -- ) create  here  12 cells dup  allot  0 fill
+  does> ( -- a ) bit @  cells +  1 bit +! ;
+pops p
+: do-cr ( -- ) bit @ 0= if  r> drop  else  0 bit !  1 n +!  then ;
+: go ( -- ) begin key dup  10 = if drop do-cr else 48 -  p +!  then again ;
+: gamma ( -- g ) 0  12 0 do  1 <<  p @ 2*  n @ >  1 and  or  loop ;
+: delta ( g -- g d ) dup  invert  1 12 << 1-  and ;
+go gamma delta *
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advent-2021-03b.fs

+\ Fill PAD with raw chars read from problem input, with 12 char stride.
+\ # of chars read: "#c".
+
+variable #c
+\ 5 constant stride
+12 constant stride
+
+: key>pad ( a n -- a' )
+  dup 32 = if  drop  pad - #c !  rdrop exit then
+  dup 10 = if drop exit then
+  over c! 1+ ;
+  
+: keys>pad ( -- ) pad begin key key>pad again ;
+
+: buf ( -- a ) pad #c @ + ;
+
+: pad>buf ( -- ) pad buf #c @ cmove> ;
+
+: stride-exec ( a #bit xt -- n )
+  >r
+  over + ( a a' )  swap  #c @ +  swap ( amax a' )
+  begin  2dup >  while
+  dup r@ execute  stride +
+  repeat
+  2drop rdrop ;
+
+variable digit-count 2 cells allot
+: strip-sign ( n -- n') cell 8 * 1- 1 swap << invert and ;
+: c-to-idx ( c -- i ) 48 - strip-sign 2 min ;
+: clear-counts ( -- ) digit-count 3 cells 0 fill ;
+: count-digit ( c -- ) c-to-idx cells digit-count +  1 swap +! ;
+
+: (most-common-step) ( a -- ) c@ count-digit ;
+: (most-common-end) ( -- n ) digit-count 2@ >= 1 and ;
+: most-common ( a #bit -- n )
+  clear-counts
+  ['] (most-common-step)  stride-exec  (most-common-end) ;
+
+: least-common ( a #bit -- n ) most-common 1 xor ;
+
+variable bit-offset
+variable savior-char
+create last-saved stride allot
+: (nuke) ( a -- ) bit-offset @ -  stride  bl  fill ;
+: (save) ( a -- ) bit-offset @ -  last-saved  stride  cmove> ;
+: (nuke-step) ( a -- ) dup c@  savior-char @  =  if (save) else (nuke) then ;
+: nuke ( a #bit savior-bit -- )
+  48 + savior-char !
+  dup bit-offset !
+  ['] (nuke-step)  stride-exec ;
+
+: ox ( -- ) pad>buf buf  stride 0 do  dup i 2dup most-common nuke  loop  drop ;
+: co ( -- ) pad>buf buf  stride 0 do  dup i 2dup least-common nuke  loop  drop ;
+: ans>num ( -- n ) 0 0 last-saved stride  >number  2drop drop ;
+
+: go ( -- ) keys>pad binary  ox ans>num  co ans>num  decimal * ." Answer:" . ;
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