Solve 2017 day 14 to 17.

2017/d16.py

@@ -0,0 +1,60 @@
+from lib import LETTERS_LOWER, str_to_int, str_to_ints
+ 
+
+def one_cycle(xs, insts):
+    for inst in insts:
+        if inst.startswith("s"):
+            v = str_to_int(inst)
+            if v != 0:
+                xs = xs[-v:] + xs[:len(xs) - v]
+        elif inst.startswith("x"):
+            a, b = str_to_ints(inst)
+            xs[a], xs[b] = xs[b], xs[a]
+        elif inst.startswith("p"):
+            la, lb = inst[1], inst[3]
+            a, b = xs.index(la), xs.index(lb)
+            xs[a], xs[b] = xs[b], xs[a]
+        else:
+            assert False
+    return xs
+
+
+def part_1(data):
+    xs = list(LETTERS_LOWER[:16])
+    insts = data.split(",")
+    xs = one_cycle(xs, insts)
+    r = "".join(xs)
+    print(r)
+
+
+def part_2(data):
+    repeat = 10**9
+    xs = list(LETTERS_LOWER[:16])
+    insts = data.split(",")
+    cycle = 0
+    seen = {}
+    for i in range(repeat):
+        xs = one_cycle(xs, insts)
+        xst = tuple(xs)
+        if not xst in seen:
+            seen[xst] = i
+        else:
+            cycle = (i - seen[xst])
+            break
+
+    xs = list(LETTERS_LOWER[:16])
+    repeat %= cycle
+    for i in range(repeat):
+        xs = one_cycle(xs, insts)
+    r = "".join(xs)
+    print(r)
+
+
+def main():
+    data = open(0).read().strip()
+    part_1(data)
+    part_2(data)
+
+
+if __name__ == "__main__":
+    main()