index.ts

import run from "aocrunner";

const parseInput = (rawInput: string) => rawInput;

const part1 = (rawInput: string) => {
  const input = parseInput(rawInput);
  let blocks: string[] = [];

  let isFreeSpace = false;
  let idCounter = 0;
  for (const char of input) {
    for (let i = 0; i < Number(char); i++) {
      if (isFreeSpace) {
        blocks.push(".");
      } else {
        blocks.push(String(idCounter));
      }
    }
    if (!isFreeSpace) idCounter++;
    isFreeSpace = !isFreeSpace;
  }

  // slow
  // let numIndex = blocks.length - 1;
  // for (let i = 0; i < blocks.length; i++) {
  //   if (blocks[i] === ".") {
  //     for (let j = numIndex; j > 0; j--) {
  //       if (i > j) break;
  //       if (blocks[j] !== ".") {
  //         const char = blocks[j];
  //         blocks[j] = blocks[i];
  //         blocks[i] = char;
  //         numIndex--;
  //         break;
  //       }
  //     }
  //   }
  // }

  for (let i = 0; i < blocks.length; i++) {
    if (blocks[i] !== ".") continue;

    const last = blocks.pop()!;
    if (last === ".") {
      i--;
      continue;
    }

    blocks[i] = last;
  }

  let checksum: number = 0;
  for (let i = 0; i < blocks.length; i++) {
    checksum += Number(blocks[i]) * i;
  }

  return checksum;
};

const part2 = (rawInput: string) => {
  const input = parseInput(rawInput);
  let blocks: string[] = [];

  let isFreeSpace = false;
  let idCounter = 0;
  for (const char of input) {
    for (let i = 0; i < Number(char); i++) {
      if (isFreeSpace) {
        blocks.push(".");
      } else {
        blocks.push(String(idCounter));
      }
    }
    if (!isFreeSpace) idCounter++;
    isFreeSpace = !isFreeSpace;
  }
  // console.log(blocks.join(""));

  const arrLen = blocks.length;
  for (let i = arrLen - 1; i >= 0; i--) {
    const c = blocks[i];
    if (c !== ".") {
      let l = 1;
      while (c === blocks[i - l]) {
        l++;
      }
      i -= l - 1;
      // find slot
      let slotLen = 0;
      let slotStart = 0;
      for (let j = 0; j < arrLen; j++) {
        // break if i cursor passes j cursor
        if (j > i) break;
        if (blocks[j] === ".") {
          if (slotLen === 0) slotStart = j;
          slotLen++;
        } else {
          slotLen = 0;
        }
        // slot found
        if (slotLen === l) {
          // swap positions
          for (let k = 0; k < l; k++) {
            blocks[slotStart + k] = c;
            blocks[i + k] = ".";
          }
          break;
        }
      }
    }
  }

  let checksum: number = 0;
  for (let i = 0; i < blocks.length; i++) {
    if (blocks[i] !== ".") {
      checksum += Number(blocks[i]) * i;
    }
  }

  return checksum;
};

run({
  part1: {
    tests: [
      {
        input: `2333133121414131402`,
        expected: 1928,
      },
    ],
    solution: part1,
  },
  part2: {
    tests: [
      {
        input: `2333133121414131402`,
        expected: 2858,
      },
    ],
    solution: part2,
  },
  trimTestInputs: true,
  onlyTests: false,
});