irish

y2021/p18.py

+from functools import reduce
+from itertools import permutations
+
+
+text = open(0).read()
+inp = [eval(line) for line in text.splitlines()]
+
+
+def explode(state):
+    last = None
+    carry = None
+    def mut(parent, idx, depth=1):
+        nonlocal last, carry
+        if type(parent[idx]) == int:
+            last = parent, idx
+            if carry:
+                parent[idx] += carry
+                raise RuntimeError
+        elif carry is None and depth == 4:
+            x, y = parent[idx]
+            if last:
+                p, j = last
+                p[j] += x
+            carry = y
+            parent[idx] = 0
+        else:
+            mut(parent[idx], 0, depth + 1)
+            mut(parent[idx], 1, depth + 1)
+    try:
+        mut(state, 0)
+        mut(state, 1)
+    except RuntimeError:
+        pass
+    return carry is not None
+
+
+def split(state):
+    def mut(par, idx):
+        if type(par[idx]) == int:
+            N = int(par[idx])
+            if N >= 10:
+                par[idx] = [N // 2, N // 2 + (N & 1)]
+                raise RuntimeError
+        else:
+            mut(par[idx], 0)
+            mut(par[idx], 1)
+    try:
+        mut(state, 0)
+        mut(state, 1)
+    except RuntimeError:
+        return True
+
+
+def add(a, b):
+    state = eval(str([a, b]))
+    while True:
+        if explode(state):
+            continue
+        elif split(state):
+            continue
+        else:
+            break
+    return state
+
+
+def magnitude(seq):
+    if type(seq) == int:
+        return seq
+    x, y = seq
+    return 3 * magnitude(x) + 2 * magnitude(y)
+
+
+print(magnitude(reduce(add, inp)))
+print(max(magnitude(add(*pair)) for pair in permutations(inp, 2)))