Solve 2016 day 21.

2016/d21.py

@@ -0,0 +1,66 @@
+from itertools import permutations
+
+
+def part_1(data, text):
+    text = list(text)
+    for line in data.splitlines():
+        words = line.split()
+        # print(text)
+        # print(words)
+        match words:
+            case ["move", "position", a, "to", "position", b]:
+                l = text.pop(int(a))
+                text.insert(int(b), l)
+            case ["rotate", "right", a, "steps"] | ["rotate", "right", a, "step"]:
+                a = int(a)
+                ntext = list(text)
+                for i in range(len(text)):
+                    ntext[(i + a) % len(text)] = text[i]
+                text = ntext
+            case ["rotate", "left", a, "steps"] | ["rotate", "left", a, "step"]:
+                a = int(a)
+                ntext = list(text)
+                for i in range(len(text)):
+                    ntext[(i - a) % len(text)] = text[i % len(text)]
+                text = ntext
+            case ["swap", "letter", a, "with", "letter", b]:
+                ia = text.index(a)
+                ib = text.index(b)
+                text[ia], text[ib] = text[ib], text[ia]
+            case ["swap", "position", a, "with", "position", b]:
+                ia, ib = int(a), int(b)
+                text[ia], text[ib] = text[ib], text[ia]
+            case ["reverse", "positions", a, "through", b]:
+                a, b = int(a), int(b)
+                assert b > a
+                text[a:b + 1] = reversed(text[a:b + 1])
+            case ["rotate", "based", "on", "position", "of", "letter", c]:
+                i = text.index(c)
+                a = 1 + i + (1 if i >= 4 else 0)
+                ntext = list(text)
+                for i in range(len(text)):
+                    ntext[(i + a) % len(text)] = text[i % len(text)]
+                text = ntext
+            case _:
+                assert False
+    return "".join(text)
+
+
+def part_2(data):
+    pw = "fbgdceah"
+    for p in permutations(pw):
+        if part_1(data, p) == pw:
+            print("".join(p))
+            return
+
+
+def main():
+    data = open(0).read().strip()
+    print(part_1(data, "abcdefgh"))
+    part_2(data)
+
+
+if __name__ == "__main__":
+    main()
+
+

README.md

@@ -53,7 +53,8 @@ written in Python.
 - Day 18: 9:43
 - Day 19: 90:00 that wasn't easy for me
 - Day 20: 67:00
-- Day 21:
+- Day 21: 32:33
+- Day 22: 
 
 
 # 2017