Day 25

input/25.txt

@@ -0,0 +1,127 @@
+1---210=1=02-202
+2--200=0112-
+112=2=200=02=
+11-1
+1=1=112011=2===
+2-=11==1
+1==210-00=0=
+1-2===-11--0-020
+111==121==--
+1-=2-11-112
+1=-10-10-11
+1=21101==100=0-01
+1222=0=22=1==1=
+122-==-22
+2=-=02
+101-2-01
+122-
+2=111-22-2=202-001
+1=1=
+10=2
+2-22-0=20-11
+2=-22-10
+1=1
+10-==-=01202=0101
+121212101012=1
+1=2212=2-022021=
+2=00=10--2-020-=20
+1-0222-22-
+1=011
+1120--2-=1=22=1
+102==2----1
+11=1020=0--102==0-
+12--0-11-21--1=2
+220-01010-111
+2=2=1=0=1-001-2
+1--0-=
+1111-01
+1-2=-1=1221-00==1=1
+1-=0-00----022121=0=
+2-
+2-111200=2-12-0
+1002-002
+2020
+110=12==--1=12=2==
+102-11122--0
+2=-=2-=1===11
+110=20
+2--12
+1=-2-1=01=
+11122=211
+1-0002
+1==1=21011=
+1=0-00122
+1---0112-=222
+2-222120=-
+1000
+2-010=-0-
+20=12000202221
+1120=2=21-2
+12==-1
+2=2==11=10=0
+1-0-001=-2
+20==2-02==--=101
+111001--20102
+121=21
+1=1-==2-=121
+10100==0=
+2=
+1=-0=20---=-02=1==
+1-0=12=0=2=12
+21---2---2
+12=-=--=0
+2=002--=10
+1=1=-21==010=1-=2-
+1=-10--=
+20022-1---1-211
+1=
+1-102==2=2000
+22-0222-
+1120=1=202=0110-000
+220102==0-
+10001=====1--1-=02
+2012-0=1=1=21210-2
+1-=1-0-0=-
+21212-==01-1=
+22222=
+1--21==1-1-101-022
+111
+1-000212
+1-1=20=
+1-21
+212====-1
+1==
+2-===2-10=110=
+1--22
+1=0-10010=12==100=
+201-
+1=1000220=12
+21--=-2
+10-0-200=1-0122
+2100222==20-=1-10
+100=11111121=1
+2110
+21201-1
+120=2-1--120001
+1==1=01100112
+11101
+1-=1=0
+2-=2
+10
+122=020221220-0
+2==21
+10=1011=1011
+11=02
+2210=---=0-
+212
+2010-0202=22
+112-121111=2
+101112-0-1=00
+10==-=-20=-112===0
+1=0-10-0
+1=11-0=--110020=
+20212--=-=01-11=
+1==0-=0
+10-21010022110-
+10--12=000
+10=0

src/25.rkt

@@ -0,0 +1,30 @@
+#lang racket
+
+(require "../lib.rkt")
+
+(define (snafu->number s)
+  (for/sum ([c (reverse (string->list s))]
+            [n (in-naturals)])
+    (* (expt 5 n)
+       (match c
+         [#\= -2]
+         [#\- -1]
+         [_ (char->number c)]))))
+
+(define (number->snafu n)
+  (let loop ([n n]
+             [cs '()])
+    (if (zero? n) (list->string cs)
+        (match (% n 5)
+          [4 (loop (/ (+ n 1) 5) (cons #\- cs))]
+          [3 (loop (/ (+ n 2) 5) (cons #\= cs))]
+          [2 (loop (/ (- n 2) 5) (cons #\2 cs))]
+          [1 (loop (/ (- n 1) 5) (cons #\1 cs))]
+          [0 (loop (/ n 5) (cons #\0 cs))]))))
+
+(define part1
+  (number->snafu
+   (for/sum ([req (problem-input 25)])
+     (snafu->number req))))
+
+(show-solution part1 #f)