Add Advent 2021 - day 18.

Lots and lots of recursion.

test6.txt is my puzzle input.

2021/day18/p.rkt

@@ -0,0 +1,95 @@
+#lang racket/base
+(require racket/string)
+(require racket/match)
+
+(define slist
+  (let-values ([(in out) (make-pipe)])
+    (for/list ([t (in-lines)])
+      (display (string-replace t "," " . ") out)
+      (read in))))
+
+(define (reduce-number v)
+  (define (get-explosion vl depth position)
+    (define explode (= depth 4))
+    (define (recurse fn p)
+      (let* ([nc (fn vl)]
+             [np (add1 p)])
+        (if (pair? nc)
+            (get-explosion nc (add1 depth) p)
+            (begin
+              ;(printf "nc np ~a ~a~n" nc np)
+              (values explode np nc (cdr vl))))))
+    (match/values (recurse car position)
+                  [(#t p a b) (values #t p a b)]
+                  [(#f p a b) (recurse cdr p)]))
+
+  (define-values (explode where-explode v1 v2) (get-explosion v 0 0))
+  ;(printf "explosion ~a ~a~n" explode where-explode)
+
+  (define (traverse-number vl position)
+    ;(printf "~a ~a~n" vl position)
+    (define (recurse fn p)
+      (let* ([nc (fn vl)]
+             [np (add1 p)])
+        ;(printf "pair ~a~n" nc)
+        (if (pair? nc)
+            (traverse-number nc p)
+            (values
+             (if (not explode)
+                 nc
+                 (if (= (- where-explode 2) p)
+                     (+ v1 nc)
+                     (if (= (+ 1 where-explode) p)
+                         (+ v2 nc)
+                         nc)))
+             np))))
+
+    (if (and explode (not (pair? (car vl))) (not (pair? (cdr vl))) (= (add1 position) where-explode))
+        (values 0 (+ 2 position))
+        (let*-values ([(r p) (recurse car position)]
+                      [(l p) (recurse cdr p)])
+          ;(printf "new cons ~a ~a ~n" r l)
+          (values (cons r l) p))))
+
+  (define can-do #t)
+  (define (split-number vl)
+    (define (recurse fn)
+      (let ([nc (fn vl)])
+        (if (pair? nc)
+            (split-number nc)
+            (if (and can-do (>= nc 10))
+                (let ([rdiv (/ nc 2)])
+                  (set! can-do #f)
+                  (cons (floor rdiv) (ceiling rdiv)))
+                nc))))
+    (cons
+     (recurse car)
+     (recurse cdr)))
+
+  (let-values ([(nv p) (traverse-number v 0)])
+    (if (equal? nv v)
+        (let ([nv (split-number v)])
+          (if (equal? nv v)
+              v
+              (reduce-number nv)))
+        (reduce-number nv))))
+
+(define (add-values v l)
+  (if (null? l)
+      v
+      (add-values (reduce-number (cons v (car l))) (cdr l))))
+
+(define (magnitude-number v)
+  (define (recurse fn)
+    (let ([nc (fn v)])
+      (if (pair? nc)
+          (magnitude-number nc)
+          nc)))
+  (+ (* 3 (recurse car)) (* 2 (recurse cdr))))
+
+; part 1
+(magnitude-number (add-values (car slist) (cdr slist)))
+
+; part 2
+(apply max (for*/list ([v1 slist] [v2 slist] #:unless (equal? v1 v2))
+             (magnitude-number (add-values v1 (list v2)))))

2021/day18/test1.txt

@@ -0,0 +1,5 @@
+[1 . 1]
+[2 . 2]
+[3 . 3]
+[4 . 4]
+[5 . 5]

2021/day18/test2.txt

@@ -0,0 +1,6 @@
+[1,1]
+[2,2]
+[3,3]
+[4,4]
+[5,5]
+[6,6]

2021/day18/test3.txt

@@ -0,0 +1,10 @@
+[[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]]
+[7,[[[3,7],[4,3]],[[6,3],[8,8]]]]
+[[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]]
+[[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]]
+[7,[5,[[3,8],[1,4]]]]
+[[2,[2,2]],[8,[8,1]]]
+[2,9]
+[1,[[[9,3],9],[[9,0],[0,7]]]]
+[[[5,[7,4]],7],1]
+[[[[4,2],2],6],[8,7]]

2021/day18/test4.txt

@@ -0,0 +1,2 @@
+[[[[4,3],4],4],[7,[[8,4],9]]]
+[1,1]

2021/day18/test5.txt

@@ -0,0 +1,10 @@
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]

2021/day18/test6.txt

@@ -0,0 +1,100 @@
+[[[7,1],2],3]
+[[1,7],7]
+[[6,8],[[6,[3,6]],[0,5]]]
+[[[[2,1],8],[[9,4],8]],[[6,5],4]]
+[[1,[[3,8],[9,1]]],[[9,1],[[1,7],0]]]
+[[[7,4],[8,[7,6]]],[9,[[6,3],[7,8]]]]
+[[[[5,0],1],4],[[5,[6,9]],[[4,3],2]]]
+[[[3,8],8],[[[3,2],8],[9,[0,5]]]]
+[[[[5,8],[3,9]],[7,[1,4]]],[6,1]]
+[3,[[[3,3],9],[0,7]]]
+[[[6,9],1],[[0,[8,4]],[[2,2],9]]]
+[[[[6,2],3],[0,4]],3]
+[[[[3,8],7],[[7,4],0]],[2,[5,[2,8]]]]
+[[4,[9,[8,0]]],[[1,5],[[9,3],8]]]
+[[[8,5],[3,[1,4]]],[[6,[8,0]],[[2,7],[2,6]]]]
+[4,7]
+[[[[2,3],0],[[1,9],[4,1]]],[[1,[4,2]],3]]
+[[[8,[5,3]],[[5,7],7]],[[5,6],[6,4]]]
+[[[[2,4],1],[8,6]],[[6,5],[0,[9,1]]]]
+[[[1,[5,7]],8],[[[9,1],9],[[1,2],4]]]
+[[[[5,5],[4,0]],[4,[9,6]]],[[[2,1],1],7]]
+[[[[1,9],[9,5]],[[5,0],[3,1]]],[[[6,7],[8,8]],[[7,3],0]]]
+[[6,[[6,7],[9,0]]],[[7,7],[[0,3],0]]]
+[[0,6],[5,2]]
+[[[[5,8],3],[[9,0],8]],[7,4]]
+[[0,[[9,9],[9,4]]],[[[1,1],2],[1,[6,7]]]]
+[0,[[5,7],2]]
+[[2,[[5,4],6]],[1,[8,[7,6]]]]
+[[[1,7],[8,[5,8]]],[[[2,1],[9,1]],[[5,6],9]]]
+[[1,8],[9,[4,3]]]
+[5,[2,[[5,5],9]]]
+[3,[8,[[2,8],[4,8]]]]
+[[[4,9],[[5,5],0]],[9,[8,[3,0]]]]
+[[[2,[6,4]],[8,[9,9]]],[[[0,4],8],[3,[9,7]]]]
+[[[[8,1],[2,4]],3],[1,[[3,3],[6,3]]]]
+[[[8,[7,3]],[1,8]],2]
+[[8,[8,4]],[[6,[4,7]],[3,0]]]
+[[[[4,6],[8,3]],9],[9,[[8,9],[0,9]]]]
+[[3,[[2,7],[4,4]]],2]
+[8,[[[8,6],2],[[8,9],6]]]
+[[[[5,7],[2,0]],[[0,2],[5,5]]],[[[8,5],5],[[1,3],[2,3]]]]
+[[1,6],[[9,8],[9,[4,9]]]]
+[[[[1,4],5],9],[4,[6,8]]]
+[[[[6,4],[9,0]],[[1,4],[6,6]]],[[9,[2,8]],2]]
+[[[[5,9],2],[[0,0],5]],[2,1]]
+[6,[[3,2],[[3,0],0]]]
+[[[[7,4],1],[[4,1],1]],[[3,4],4]]
+[3,[9,[9,7]]]
+[[[3,[3,3]],[0,3]],[1,[1,8]]]
+[[8,[8,7]],[[9,2],5]]
+[[[1,[3,9]],[5,9]],[1,5]]
+[[[[7,8],[9,7]],9],[[[9,2],[2,2]],[[9,6],8]]]
+[4,[[3,5],[[1,3],[5,5]]]]
+[7,[[[0,1],2],[[3,6],5]]]
+[0,[[[2,4],[3,4]],[8,9]]]
+[[1,[[6,8],1]],[8,0]]
+[1,1]
+[7,0]
+[[1,2],[[0,[8,3]],[[4,5],[9,7]]]]
+[[[[2,3],[5,9]],[7,[1,9]]],2]
+[[3,5],[[9,7],9]]
+[[[[6,9],[4,8]],6],0]
+[[[[2,4],[3,9]],[2,[9,4]]],[[[8,9],[3,1]],7]]
+[[5,[[0,2],4]],[[[9,9],[7,4]],[1,5]]]
+[3,[6,[[5,4],1]]]
+[[[2,[2,7]],2],[[4,[7,3]],5]]
+[7,[[0,[2,0]],[[9,4],6]]]
+[[4,[3,[6,2]]],9]
+[[[0,[5,6]],[8,3]],[[7,9],[0,[9,6]]]]
+[8,[[6,4],[4,8]]]
+[[[8,[6,8]],[5,[7,3]]],[[[7,8],5],2]]
+[[[[3,5],[4,7]],5],[[0,0],[9,[1,9]]]]
+[[7,[[1,5],9]],[[[3,4],[1,7]],[1,[7,9]]]]
+[[0,[3,[4,1]]],[[[2,9],3],[4,[0,8]]]]
+[[[8,[1,6]],[[0,1],7]],[[[1,1],[0,2]],[[9,4],[9,6]]]]
+[[[[6,7],0],[[6,8],9]],[[1,[6,6]],[[2,9],[4,7]]]]
+[[[[5,0],[1,2]],[1,[5,1]]],[[0,4],1]]
+[[9,1],6]
+[[7,2],[[[5,5],[4,3]],6]]
+[[9,[[0,6],9]],[[7,9],[7,1]]]
+[[[[7,3],[6,4]],[[2,5],[7,2]]],[[[4,4],0],[[9,5],[8,5]]]]
+[[[[8,8],[6,4]],[[0,2],[9,5]]],2]
+[[[[3,0],7],[9,2]],[[0,[8,6]],[[7,2],[8,5]]]]
+[[0,6],[1,[9,[4,3]]]]
+[[0,8],[[[5,0],6],[5,[2,0]]]]
+[[[[7,1],[0,3]],[[9,9],[3,5]]],[4,[8,4]]]
+[7,[[1,[3,7]],[[3,4],[2,3]]]]
+[[[[2,2],[4,8]],[[3,4],0]],[[[1,5],[2,8]],5]]
+[6,[[[9,1],5],[9,9]]]
+[[[2,[8,6]],[[9,9],[6,3]]],4]
+[[[[3,2],[9,3]],8],9]
+[[[[6,9],0],[[0,6],[1,3]]],[[5,[9,8]],[[1,5],[3,7]]]]
+[[2,[4,[2,3]]],[[[6,0],[7,2]],3]]
+[[[[8,3],4],[6,[8,8]]],4]
+[[[9,8],5],[[[4,4],[6,3]],[8,6]]]
+[9,2]
+[[[3,4],[4,[7,0]]],[0,[4,[6,9]]]]
+[[[0,8],[3,9]],[[[3,8],6],[[9,3],6]]]
+[[[[5,6],[0,3]],1],[8,[2,9]]]
+[[[[4,2],8],[[9,3],7]],0]