day10.js

const fs = require("fs");

const lines = fs
  .readFileSync("day10.txt", { encoding: "utf-8" }) // read day??.txt content
  .replace(/\r/g, "") // remove all \r characters to avoid issues on Windows
  .split("\n") // Split on newline
  .filter(Boolean); // Remove empty lines

function median(array) {
  //taken from day 7
  const internalArray = [...array];
  internalArray.sort((a, b) => a - b);
  if (internalArray.length % 2 === 0) {
    return (
      (internalArray[internalArray.length / 2 - 1] +
        internalArray[internalArray.length / 2]) /
      2
    );
  } else {
    return internalArray[Math.floor(internalArray.length / 2)];
  }
}

function part1() {
  const closingChar = {
    "(": ")",
    "{": "}",
    "[": "]",
    "<": ">",
  };
  const point = {
    ")": 3,
    "]": 57,
    "}": 1197,
    ">": 25137,
  };
  const found = {
    ")": 0,
    "]": 0,
    "}": 0,
    ">": 0,
  };

  for (const line of lines) {
    const stack = [];
    for (let i = 0; i < line.length; i++) {
      const element = line[i];
      if (/[({\[<]/.test(element)) {
        stack.push(closingChar[element]);
      } else {
        const expected = stack.pop();
        if (expected !== element) {
          //corrupted line
          found[element]++;
          break;
        }
      }
    }
  }

  const score = Object.keys(found)
    .map((key) => point[key] * found[key])
    .reduce((a, b) => a + b, 0);
  console.log(score);
}

part1();

function part2() {
  const closingChar = {
    "(": ")",
    "{": "}",
    "[": "]",
    "<": ">",
  };
  const points = {
    ")": 1,
    "]": 2,
    "}": 3,
    ">": 4,
  };
  const scores = [];

  for (const line of lines) {
    const stack = [];
    let corrupted = false;
    for (let i = 0; i < line.length; i++) {
      const element = line[i];
      if (/[({\[<]/.test(element)) {
        stack.push(closingChar[element]);
      } else {
        const expected = stack.pop();
        if (expected !== element) {
          //corrupted line
          corrupted = true;
          break;
        }
      }
    }
    if (!corrupted && stack.length > 0) {
      // incomplete line
      const closingChars = stack.reverse().join("");
      let score = 0;
      for (let i = 0; i < closingChars.length; i++) {
        const element = closingChars[i];
        score *= 5;
        score += points[element];
      }
      scores.push(score);
    }
  }
  console.log(median(scores));
}

part2();