Implement days 20 and 21.

README.md

@@ -24,3 +24,5 @@
   LEADERBOARD?!?!?!?!?!?!?!
 - Day 17: Second one was fun with having to detect the repetition.
 - Day 18: 12:00 and 32:00; really straightforward and of course way too slow.
+- Day 19: Slow.
+- Day 20: Struggled way too much.

d20.py

@@ -0,0 +1,73 @@
+from lib import *
+
+EXAMPLE = """1
+2
+-3
+3
+-2
+0
+4
+"""
+
+
+def move(xs, i, move):
+    move = move % (len(xs) - 1)
+    ni = (i + move + 1) % len(xs)
+    xsi, xs[i] = xs[i], None
+    xs.insert(ni, xsi)
+    xs.remove(None)
+    return xs
+
+
+def asserts():
+    assert move([1, 2, 3], 0, 0) == [1, 2, 3]
+    assert move([1, 2, 3], 0, 1) == [2, 1, 3]
+    assert move([1, 2, 3], 0, 2) == [1, 2, 3]
+    assert move([1, 2, 3], 0, 3) == [2, 1, 3]
+    assert move([1, 2, 3], 0, 4) == [1, 2, 3]
+    assert move([1, 2, 3], 0, 5) == [2, 1, 3]
+    assert move([1, 2, 3], 0, 2) == [1, 2, 3]
+    assert move([3, 2, 1], 2, 1) == [3, 1, 2]
+    assert move([3, 2, 1], 2, 2) == [1, 3, 2]
+
+    assert move([4, -2, 5, 6, 7, 8, 9,], 1, -2) == [4, 5, 6, 7, 8, -2, 9]
+    assert move([1, 2, -2, -3, 0, 3, 4], 2, -2) == [-2, 1, 2, -3, 0, 3, 4]
+
+
+def solve(input: Input, second=False):
+    xs = list(map(int, input.lines()))
+    if second:
+        xs = list(map(lambda n: n * 811589153, xs))
+    ys = list(range(len(xs)))
+    oys = ys[:]
+
+    repeat = 1
+    if second:
+        repeat = 10
+    for _ in range(repeat):
+        for o in oys:
+            i = ys.index(o)
+            movev = xs[o]
+            move(ys, i, movev)
+
+    xs = [xs[i] for i in ys]
+    s = 0
+    i0 = xs.index(0)
+    for i in range(1, 4):
+        ni = (i0 + i * 1000) % len(ys)
+        s += xs[ni]
+    return s
+
+
+def main():
+    DAY_INPUT = "i20.txt"
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    assert solve(Input(DAY_INPUT), True) == 6704537992933
+
+
+if __name__ == "__main__":
+    asserts()
+    main()

d21.py

@@ -0,0 +1,105 @@
+from lib import *
+
+EXAMPLE = """root: pppw + sjmn
+dbpl: 5
+cczh: sllz + lgvd
+zczc: 2
+ptdq: humn - dvpt
+dvpt: 3
+lfqf: 4
+humn: 5
+ljgn: 2
+sjmn: drzm * dbpl
+sllz: 4
+pppw: cczh / lfqf
+lgvd: ljgn * ptdq
+drzm: hmdt - zczc
+hmdt: 32
+"""
+
+def resolve(monkeys, s):
+    equ = monkeys[s]
+    try:
+        return int(equ)
+    except ValueError:
+        pass
+    l, op, r = equ.split(" ")
+    l = resolve(monkeys, l)
+    r = resolve(monkeys, r)
+    res = eval(f"{l}{op}{r}")
+    monkeys[s] = res
+    return res
+
+
+def resolve2(monkeys, s):
+    if s == "humn":
+        return tuple()
+
+    equ = monkeys[s]
+    try:
+        return int(equ)
+    except ValueError:
+        pass
+
+    l, op, r = equ.split(" ")
+    if s == "root":
+        op = "=="
+
+    l = resolve2(monkeys, l)
+    r = resolve2(monkeys, r)
+
+    if isinstance(l, tuple) or isinstance(r, tuple):
+        return (l, op, r)
+    if op == "/":
+        op = "//"
+    res = eval(f"{l}{op}{r}")
+    monkeys[s] = res
+    return res
+
+
+def simplify(equ, exp):
+    if equ == tuple():
+        return exp
+    l, op, r = equ
+    if op == '/' and isinstance(r, int):
+        return simplify(l, exp * r)
+    elif op == '+' and isinstance(l, int):
+        return simplify(r, exp - l)
+    elif op == '+' and isinstance(r, int):
+        return simplify(l, exp - r)
+    elif op == '-' and isinstance(l, int):
+        return simplify(r, -(exp - l))
+    elif op == '-' and isinstance(r, int):
+        return simplify(l, exp + r)
+    elif op == '*' and isinstance(r, int):
+        return simplify(l, exp // r)
+    elif op == '*' and isinstance(l, int):
+        return simplify(r, exp // l)
+
+
+def solve(input: Input, second=False):
+    res = 0
+    monkeys = {}
+    for line in input.lines():
+        l, r = line.split(": ")
+        monkeys[l] = r
+
+    if not second:
+        return int(resolve(monkeys, "root"))
+    else:
+        equ = resolve2(monkeys, "root")
+        assert equ[1] == '=='
+        return simplify(equ[0], equ[2])
+
+
+def main():
+    DAY_INPUT = "i21.txt"
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    assert solve(Input(DAY_INPUT), True) == 3243420789721
+
+
+if __name__ == "__main__":
+    main()