protohackers/2.ts

import { BufReader } from "https://deno.land/std@0.157.0/io/buffer.ts";
import { ByteSet } from "https://deno.land/x/bytes@1.0.3/mod.ts";

const QUERY_SIZE = 9;
const PORT = 5588;

const listener = Deno.listen({ port: 5588 });

console.log(`Listening on port ${PORT}`);

for await (const conn of listener) {
  console.log("Connection established:", conn.remoteAddr);
  try {
    meansToAnEnd(conn);
  } catch (e) {
    console.error(conn.remoteAddr, e);
  }
  console.log("Connection closed:", conn.remoteAddr);
}

async function meansToAnEnd(conn: Deno.Conn) {
  try {
    const prices = [];
    for await (const query of queries(conn)) {
      if (query == null) break;
      const bs = ByteSet.from(query, "big");
      const queryChar = String.fromCharCode(bs.read.uint8());
      const a1 = bs.read.int32();
      const a2 = bs.read.int32();
      if (queryChar == "I") {
        prices.push([a1, a2]);
      } else if (queryChar == "Q") {
        let numMatches = 0;
        let sum = 0;
        for (const [ts, price] of prices) {
          if (ts < a1 || ts > a2) continue;
          numMatches++;
          sum += price;
        }
        let result = Math.floor(sum / numMatches);
        if (isNaN(result)) result = 0;
        console.log(
          conn.remoteAddr,
          `Result for ${prices.length} prices: ${sum} / ${numMatches} = ${result}`,
        );
        const response = new ByteSet(4, "big");
        response.write.int32(result);
        conn.write(response.buffer);
      }
    }
    console.log("Done!");
  } catch (err) {
    console.error("Error processing query:", err);
  }
}

function queries(conn: Deno.Conn) {
  return {
    async *[Symbol.asyncIterator]() {
      const b = new Uint8Array(9);
      const reader = new BufReader(conn, QUERY_SIZE);
      try {
        while (await reader.readFull(b) != null) {
          yield b;
        }
      } catch (err) {
        console.error("Error receiving query:", err);
      }
    },
  };
}