AoC 2020.1 p1

5 files changed, 438 insertions, 0 deletions

diff --git a/report-repair/README.org b/report-repair/README.org
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+See: https://adventofcode.com/2020/day/1
+** Part 1
+*** Purpose
+Given a list of numbers (report):
+
+#+begin_example
+1721
+979
+366
+299
+675
+1456
+#+end_example
+
+This program takes two entries that sum to 2020 (in the above example, it is 1721 and 299) and multiplies them together.
+
+*** Method
+
+To do this, the program takes the full list of numbers and subtracts them from 2020:
+
+#+begin_example
+299
+1041
+1654
+1721
+1345
+564
+#+end_example
+
+It stores this as a list of cons pairs:
+
+#+begin_example
+'((299 . 1721)
+ (1041 . 979)
+ (1654 . 366)
+ (1721 . 299)
+ (1345 . 675)
+ (564 . 1456))
+#+end_example
+
+Now, we find a pair that is equivalent on the basis of containing the same elements, and complete the multiplication.
+
+** Part 2
+*** Purpose
+Of course, we now need to find three numbers in the list that meet the same criteria...
+
+Say we have a list:
+
+#+begin_example
+979
+366
+675
+#+end_example
+
+We calculate a list of key-value pairs---each number added to every other number...
+
+#+begin_example
+'((((979 366) . 1345)
+   ((979 675) . 1654)
+   ((366 675) . 1041))
+#+end_example
+
+Then, we perform the same operation as we did in the first part:
+
+#+begin_example
+'((((979 366 675) . 1345)
+   ((979 675 366) . 1654)
+   ((366 675 979) . 1041)))
+#+end_example
+
+And we simply check if all three values in the car position are in the original set of numbers.
diff --git a/report-repair/input.txt b/report-repair/input.txt
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+1941
+1887
+1851
+1874
+1612
+1960
+1971
+1983
+1406
+1966
+1554
+1892
+1898
+1926
+1081
+1992
+1073
+1603
+177
+1747
+1063
+1969
+1659
+1303
+1759
+1853
+1107
+1818
+1672
+1352
+2002
+1838
+1985
+1860
+1141
+1903
+1334
+1489
+1178
+1823
+1499
+1951
+1225
+1503
+1417
+1724
+1165
+1339
+1816
+1504
+1588
+1997
+1946
+1324
+1771
+1982
+1272
+1367
+1439
+1252
+1902
+1940
+1333
+1750
+1512
+1538
+1168
+2001
+1797
+1233
+972
+1306
+1835
+1825
+1822
+1880
+1732
+1785
+1727
+1275
+1355
+1793
+1485
+1297
+1932
+1519
+1587
+1382
+1914
+1745
+1087
+1996
+1746
+1962
+1573
+2008
+1868
+1278
+1386
+1238
+1242
+1170
+1476
+1161
+1754
+1807
+1514
+1189
+1916
+1884
+1535
+1217
+1911
+1861
+1493
+1409
+1783
+1222
+1955
+1673
+1502
+607
+2010
+1846
+1819
+1500
+1799
+1475
+1146
+1608
+1806
+1660
+1618
+1904
+978
+1762
+1925
+1185
+1154
+1239
+1843
+1986
+533
+1509
+1913
+287
+1707
+1115
+1699
+1859
+1077
+1915
+1412
+1360
+1646
+1973
+1627
+1755
+1748
+1769
+1886
+1422
+1686
+950
+100
+1372
+1068
+1370
+1428
+1870
+1108
+190
+1891
+1794
+1228
+1128
+1365
+1740
+1888
+1460
+1758
+1906
+1917
+1989
+1251
+1866
+1560
+1921
+1777
+1102
+1850
+1498
+683
+1840
+1800
+1112
+1908
+1442
+1082
+1071
diff --git a/report-repair/main.scm b/report-repair/main.scm
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+#!/run/current-system/profile/bin/guile \
+-e main -s
+!#
+
+(use-modules (rr)
+	     ((ice-9 rdelim))
+	     (ice-9 binary-ports))
+
+
+(define (stdin-to-str)
+  (let loop ((result ""))
+    (let ((line (read-line)))
+      (if (eof-object? line)
+	  result
+	  (loop (string-append result line " "))))))
+
+(define (main args)
+  (display (rr (stdin-to-str)))
+  (newline))
diff --git a/report-repair/rr-test.scm b/report-repair/rr-test.scm
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+;; -*- compile-command: "guile -L . rr-test.scm"; -*-
+(use-modules (srfi srfi-64)
+	     (rr))
+
+(test-begin "harness")
+
+
+(test-equal "friendship 1"
+  '(1 . 2019)
+  (return-friendship-pair 1))
+
+(test-equal "friendship 1596"
+  '(1596 . 424)
+  (return-friendship-pair 1596))
+
+(test-equal "small report"
+  '((0 . 2020)
+    (1 . 2019)
+    (2 . 2018)
+    (3 . 2017)
+    (4 . 2016)
+    (5 . 2015))
+  (report->pairs "0 1 2 3 4 5"))
+
+(test-assert "equivalent pair"
+  (equivalent-pair?
+   '(1 . 4)
+   '((5 . 6)
+     (1 . 5)
+     (3 . 7)
+     (4 . 1)
+     (6 . 2))))
+
+(test-equal "no equivalent pair"
+  #f
+  (equivalent-pair?
+   '(1 . 4)
+   '((5 . 6)
+     (1 . 5)
+     (3 . 7)
+     (6 . 2))))
+
+(test-equal "found equivalent pair"
+  '(1 . 5)
+  (return-equivalent-pair
+   '((5 . 6)
+     (1 . 5)
+     (3 . 7)
+     (5 . 1)
+     (6 . 2))))
+
+(test-error "no equivalent pairs"
+	    #t
+	    (return-equivalent-pair
+	     '((5 . 6)
+	       (1 . 5)
+	       (3 . 7)
+	       (6 . 2))))
+
+(test-equal "multiply pair 1"
+  8
+  (multiply-pair (cons 1 8)))
+
+(test-equal "multiply pair 2"
+  24
+  (multiply-pair (cons 3 8)))
+
+(test-equal "task-complete 1"
+  1020099
+  (rr "1009 237 791 478 1537 1011 1628"))
+
+(test-equal "task-complete 2"
+  514579
+  (rr "1721
+979
+366
+299
+675
+1456
+"))
+
+
+(test-end "harness")
diff --git a/report-repair/rr.scm b/report-repair/rr.scm
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+#!/run/current-system/profile/bin/guile \
+-e main -s
+!#
+(define-module (rr)
+  #:use-module (srfi srfi-1)
+  #:use-module (ice-9 exceptions)
+  #:export (rr
+	    multiply-pair
+	    return-equivalent-pair
+	    equivalent-pair?
+	    return-friendship-pair
+	    report->pairs))
+
+
+(define (rr str)
+  (multiply-pair
+   (return-equivalent-pair
+    (report->pairs str))))
+
+(define (multiply-pair pair)
+  (* (car pair)
+     (cdr pair)))
+
+(define (return-equivalent-pair pairs)
+  "Given PAIRS friendship pairs, returns the
+ones that are found to be friends. Throws
+friendship-exception if no friends are found.
+
+We do NOT care if there are multiple pairs.
+Return the first one."
+  (let loop ((pair (car pairs)) (pairs (cdr pairs)))
+    (if (null? pairs)
+	(raise-exception
+	 (make-exception-with-message
+	  "Concerning lack of friendship!"))
+	(if (equivalent-pair? pair pairs)
+	    pair
+	    (loop (car pairs) (cdr pairs))))))
+
+(define (equivalent-pair? pair pairs)
+  "Given friendship pair PAIR and a list
+of other PAIRS, determines if PAIR is
+contained in PAIRS, irrespective of order"
+  (let ((r-pair (cons (cdr pair)
+		      (car pair))))
+    (any (lambda (pair)
+	   (equal? r-pair pair))
+	 pairs)))
+
+(define (report->pairs str)
+  "Given a report, convert it to a
+list of friendship pairs."
+  (let ((lst (string-split
+	      (string-trim-both str char-set:whitespace)
+	      char-set:whitespace)))
+    (map (lambda (str)
+	   (return-friendship-pair
+	    (string->number str)))
+	 lst)))
+
+(define (return-friendship-pair num)
+  "Given NUM, returns a cons pair with
+CAR as the original number and CDR as
+the companion number."
+  (cons num (- 2020 num)))