2019: d14: ex2: add solution

2019/d14/ex2/ex2.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env python
+
+import sys
+from dataclasses import dataclass
+from math import ceil
+from typing import Dict, List
+
+
+@dataclass
+class Ingredient:
+    name: str
+    quantity: int
+
+
+@dataclass
+class ReactionEquation:
+    quantity: int
+    inputs: List[Ingredient]
+
+
+Reactions = Dict[str, ReactionEquation]
+
+
+def solve_for(n: int, reactions: Reactions) -> int:
+    ore_needed = 0
+    wanted = [("FUEL", n)]
+    excess: Dict[str, int] = {}
+
+    def provide_ingredient(name: str, wanted_quantity: int) -> None:
+        nonlocal ore_needed
+        nonlocal excess
+        nonlocal wanted
+
+        if name == "ORE":
+            ore_needed += wanted_quantity  # There's no recipy for this one
+            return
+
+        if name in excess:
+            # Take from excess
+            if excess[name] > wanted_quantity:
+                excess[name] -= wanted_quantity
+                return  # Nothing left to do
+            wanted_quantity -= excess[name]
+            del excess[name]  # Took everything
+
+        if wanted_quantity == 0:  # In case we provided just enough by excess
+            return
+
+        equation = reactions[name]
+        reaction_num = ceil(wanted_quantity / equation.quantity)
+
+        for ingredient in equation.inputs:
+            needed_quantity = ingredient.quantity * reaction_num
+            provide_ingredient(ingredient.name, needed_quantity)
+
+        produced_quantity = equation.quantity * reaction_num
+        excess_quantity = produced_quantity - wanted_quantity
+        if excess_quantity > 0:
+            if name in excess:
+                excess[name] += excess_quantity
+            else:
+                excess[name] = excess_quantity
+
+    while len(wanted) != 0:
+        provide_ingredient(*(wanted.pop()))
+
+    return ore_needed
+
+
+def main() -> None:
+    reactions: Reactions = {}
+
+    def parse_react(l: str) -> None:
+        def parse_ingredient(i: str) -> Ingredient:
+            quantity, name = i.strip().split(" ")
+            return Ingredient(name, int(quantity))
+
+        input_list, output_str = l.split("=>")
+        inputs = [i for i in map(parse_ingredient, input_list.split(", "))]
+        output = parse_ingredient(output_str)
+        reactions[output.name] = ReactionEquation(output.quantity, inputs)
+
+    for line in sys.stdin.readlines():
+        parse_react(line)
+
+    for_one = solve_for(1, reactions)
+    target = 1000000000000
+    # Educated guesses about minimum and maximum fuel needed to use 'target' ORE
+    min_fuel_needed = target // for_one
+    max_fuel_needed = 2 * min_fuel_needed
+    while min_fuel_needed < max_fuel_needed:
+        # We already know that minimum value is valid, offset it by one for the search
+        mid = ceil((min_fuel_needed + max_fuel_needed) / 2)
+        mid_res = solve_for(mid, reactions)
+        if mid_res > target:
+            # Exclude the maximum that was already searched
+            max_fuel_needed = mid - 1
+        else:
+            # Keep the valid minimum value
+            min_fuel_needed = mid
+
+    print(max_fuel_needed)
+
+
+if __name__ == "__main__":
+    main()