feat: 2022 Day 16 Part 2

Author: mfulton26

2022/day/16/part/2/solve.test.ts

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+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+Valve AA has flow rate=0; tunnels lead to valves DD, II, BB
+Valve BB has flow rate=13; tunnels lead to valves CC, AA
+Valve CC has flow rate=2; tunnels lead to valves DD, BB
+Valve DD has flow rate=20; tunnels lead to valves CC, AA, EE
+Valve EE has flow rate=3; tunnels lead to valves FF, DD
+Valve FF has flow rate=0; tunnels lead to valves EE, GG
+Valve GG has flow rate=0; tunnels lead to valves FF, HH
+Valve HH has flow rate=22; tunnel leads to valve GG
+Valve II has flow rate=0; tunnels lead to valves AA, JJ
+Valve JJ has flow rate=21; tunnel leads to valve II`;
+
+  assertEquals(solve(input), 1707);
+});

2022/day/16/part/2/solve.ts

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+import subsets from "@lib/subsets.ts";
+
+type ValueGraph = ReturnType<typeof parseFlowRateGraph>;
+type Distances = ReturnType<typeof computeDistances>;
+
+const regExp =
+  /^Valve (?<id>.+) has flow rate=(?<flowRateText>\d+); tunnels? leads? to valves? (?<destinationsText>.+?)$/gm;
+
+function parseFlowRateGraph(text: string) {
+  const flowRates = new Map<string, number>();
+  const tunnels = new Map<string, string[]>();
+  for (const { groups } of text.matchAll(regExp)) {
+    const { id, flowRateText, destinationsText } = groups!;
+    flowRates.set(id, +flowRateText);
+    tunnels.set(id, destinationsText.split(", "));
+  }
+  const nodes = () => flowRates.keys();
+  const value = (valve: string) => flowRates.get(valve);
+  const connected = (valve: string) => tunnels.get(valve) ?? [];
+  return { nodes, value, connected };
+}
+
+function computeDistances(graph: ValueGraph) {
+  const result = new Map<string, Map<string, number>>();
+  {
+    for (const u of graph.nodes()) {
+      const u2 = new Map<string, number>().set(u, 0);
+      result.set(u, u2);
+      for (const v of graph.connected(u)) u2.set(v, 1), u2.set(v, 1);
+    }
+    for (const m of graph.nodes()) {
+      for (const u of graph.nodes()) {
+        const u2 = result.get(u)!;
+        const u2m = u2.get(m);
+        if (u2m === undefined) continue;
+        for (const v of graph.nodes()) {
+          const m2v = result.get(m)?.get(v);
+          if (m2v === undefined) continue;
+          const u2m2v = u2m + m2v;
+          const u2v = u2.get(v);
+          if (u2v !== undefined && u2v < u2m2v) continue;
+          u2.set(v, u2m2v);
+        }
+      }
+    }
+  }
+  return result;
+}
+
+function findMaxPressure(
+  graph: ValueGraph,
+  distances: Distances,
+  targets: Set<string>,
+) {
+  let max = 0;
+  const stack = [{
+    valve: "AA",
+    t: 26,
+    opened: new Set<string>(),
+    released: 0,
+  }];
+  while (stack.length) {
+    const { valve, t, opened, released } = stack.pop()!;
+    if (released > max) max = released;
+    if (t === 0) continue;
+    for (const destination of targets.difference(opened)) {
+      const remaining = t - distances.get(valve)!.get(destination)! - 1;
+      if (remaining < 0) continue;
+      stack.push({
+        valve: destination,
+        t: remaining,
+        opened: new Set(opened).add(destination),
+        released: released + remaining * graph.value(destination)!,
+      });
+    }
+  }
+  return max;
+}
+
+export default function solve(input: string) {
+  const flowRateGraph = parseFlowRateGraph(input);
+  const distances = computeDistances(flowRateGraph);
+  const targets = flowRateGraph.nodes()
+    .filter((valve) => flowRateGraph.value(valve))
+    .reduce((set, value) => set.add(value), new Set<string>());
+  const halfOfTargetsSize = targets.size / 2;
+  const maxPressures = new Map<string, number>();
+  for (const subtargets of subsets(targets)) {
+    const maxPressure = findMaxPressure(flowRateGraph, distances, subtargets);
+    maxPressures.set(`${[...subtargets]}`, maxPressure);
+  }
+  let max = 0;
+  for (const yourTargets of subsets(targets)) {
+    if (yourTargets.size > halfOfTargetsSize) continue;
+    const theirTargets = targets.difference(yourTargets);
+    const yourHash = `${[...yourTargets]}`, theirHash = `${[...theirTargets]}`;
+    const combined = maxPressures.get(yourHash)! + maxPressures.get(theirHash)!;
+    if (combined > max) max = combined;
+  }
+  return max;
+}