2015 day 10.

src/holt59/aoc/2015/day10.py

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+import itertools
+import sys
+
+line = sys.stdin.read().strip()
+
+# see http://www.se16.info/js/lands2.htm for the explanation of 'atoms' (or elements)
+#
+# see also https://www.youtube.com/watch?v=ea7lJkEhytA (video link from AOC) and this
+# CodeGolf answer https://codegolf.stackexchange.com/a/8479/42148
+
+# fmt: off
+atoms = [
+    ("22", (0, )),  # 0
+    ("13112221133211322112211213322112", (71, 90, 0, 19, 2, )),  # 1
+    ("312211322212221121123222112", (1, )),  # 2
+    ("111312211312113221133211322112211213322112", (31, 19, 2, )),  # 3
+    ("1321132122211322212221121123222112", (3, )),  # 4
+    ("3113112211322112211213322112", (4, )),  # 5
+    ("111312212221121123222112", (5, )),  # 6
+    ("132112211213322112", (6, )),  # 7
+    ("31121123222112", (7, )),  # 8
+    ("111213322112", (8, )),  # 9
+    ("123222112", (9, )),  # 10
+    ("3113322112", (60, 10, )),  # 11
+    ("1113222112", (11, )),  # 12
+    ("1322112", (12, )),  # 13
+    ("311311222112", (66, 13, )),  # 14
+    ("1113122112", (14, )),  # 15
+    ("132112", (15, )),  # 16
+    ("3112", (16, )),  # 17
+    ("1112", (17, )),  # 18
+    ("12", (18, )),  # 19
+    ("3113112221133112", (66, 90, 0, 19, 26, )),  # 20
+    ("11131221131112", (20, )),  # 21
+    ("13211312", (21, )),  # 22
+    ("31132", (22, )),  # 23
+    ("111311222112", (23, 13, )),  # 24
+    ("13122112", (24, )),  # 25
+    ("32112", (25, )),  # 26
+    ("11133112", (29, 26, )),  # 27
+    ("131112", (27, )),  # 28
+    ("312", (28, )),  # 29
+    ("13221133122211332", (62, 19, 88, 0, 19, 29, )),  # 30
+    ("31131122211311122113222", (66, 30, )),  # 31
+    ("11131221131211322113322112", (31, 10, )),  # 32
+    ("13211321222113222112", (32, )),  # 33
+    ("3113112211322112", (33, )),  # 34
+    ("11131221222112", (34, )),  # 35
+    ("1321122112", (35, )),  # 36
+    ("3112112", (36, )),  # 37
+    ("1112133", (37, 91, )),  # 38
+    ("12322211331222113112211", (38, 0, 19, 42, )),  # 39
+    ("1113122113322113111221131221", (67, 39, )),  # 40
+    ("13211322211312113211", (40, )),  # 41
+    ("311322113212221", (41, )),  # 42
+    ("132211331222113112211", (62, 19, 42, )),  # 43
+    ("311311222113111221131221", (66, 43, )),  # 44
+    ("111312211312113211", (44, )),  # 45
+    ("132113212221", (45, )),  # 46
+    ("3113112211", (46, )),  # 47
+    ("11131221", (47, )),  # 48
+    ("13211", (48, )),  # 49
+    ("3112221", (60, 49, )),  # 50
+    ("1322113312211", (62, 19, 50, )),  # 51
+    ("311311222113111221", (66, 51, )),  # 52
+    ("11131221131211", (52, )),  # 53
+    ("13211321", (53, )),  # 54
+    ("311311", (54, )),  # 55
+    ("11131", (55, )),  # 56
+    ("1321133112", (56, 0, 19, 26, )),  # 57
+    ("31131112", (57, )),  # 58
+    ("111312", (58, )),  # 59
+    ("132", (59, )),  # 60
+    ("311332", (60, 19, 29, )),  # 61
+    ("1113222", (61, )),  # 62
+    ("13221133112", (62, 19, 26, )),  # 63
+    ("3113112221131112", (66, 63, )),  # 64
+    ("111312211312", (64, )),  # 65
+    ("1321132", (65, )),  # 66
+    ("311311222", (66, 60, )),  # 67
+    ("11131221133112", (67, 19, 26, )),  # 68
+    ("1321131112", (68, )),  # 69
+    ("311312", (69, )),  # 70
+    ("11132", (70, )),  # 71
+    ("13112221133211322112211213322113", (71, 90, 0, 19, 73, )),  # 72
+    ("312211322212221121123222113", (72, )),  # 73
+    ("111312211312113221133211322112211213322113", (31, 19, 73, )),  # 74
+    ("1321132122211322212221121123222113", (74, )),  # 75
+    ("3113112211322112211213322113", (75, )),  # 76
+    ("111312212221121123222113", (76, )),  # 77
+    ("132112211213322113", (77, )),  # 78
+    ("31121123222113", (78, )),  # 79
+    ("111213322113", (79, )),  # 80
+    ("123222113", (80, )),  # 81
+    ("3113322113", (60, 81, )),  # 82
+    ("1113222113", (82, )),  # 83
+    ("1322113", (83, )),  # 84
+    ("311311222113", (66, 84, )),  # 85
+    ("1113122113", (85, )),  # 86
+    ("132113", (86, )),  # 87
+    ("3113", (87, )),  # 88
+    ("1113", (88, )),  # 89
+    ("13", (89, )),  # 90
+    ("3", (90, )),  # 91
+]
+# fmt: on
+
+starters = [
+    "1",
+    "11",
+    "21",
+    "1211",
+    "111221",
+    "312211",
+    "13112221",
+    "1113213211",
+    "31131211131221",
+]
+
+
+def look_and_say_length(s: str, n: int) -> int:
+    if n == 0:
+        return len(s)
+
+    if s in starters:
+        return look_and_say_length(
+            "".join(f"{len(list(g))}{k}" for k, g in itertools.groupby(s)), n - 1
+        )
+
+    counts = {i: 0 for i in range(len(atoms))}
+    idx = next(i for i, (a, _) in enumerate(atoms) if s == a)
+    counts[idx] = 1
+
+    for _ in range(n):
+        c2 = {i: 0 for i in range(len(atoms))}
+        for i in counts:
+            for j in atoms[i][1]:
+                c2[j] += counts[i]
+        counts = c2
+
+    return sum(counts[i] * len(a[0]) for i, a in enumerate(atoms))
+
+
+answer_1 = look_and_say_length(line, 40)
+print(f"answer 1 is {answer_1}")
+
+answer_2 = look_and_say_length(line, 50)
+print(f"answer 2 is {answer_2}")

src/holt59/aoc/inputs/holt59/2015/day10.txt

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+1321131112