LZW圧縮

lzw.js

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.on('line', (input) => {
  const findFirstUnregisteredIndex = (input, dict) =>
    input
      .split('')
      .findIndex((val, i, arr) => !dict.includes(arr.slice(0, i + 1).join('')));
  
  const dict = input.split('').filter((val, i) => input.indexOf(val) === i);

  const encode = (input, dict) => {
    const unregisteredIndex = findFirstUnregisteredIndex(input, dict);
    if (unregisteredIndex < 0) return [dict.indexOf(input)];
    
    const unregisteredWord = input.substr(0, unregisteredIndex + 1);
    const wordToEncode = unregisteredWord.substr(0, unregisteredWord.length - 1);
    dict.push(unregisteredWord);
    return [
      dict.indexOf(wordToEncode),
      ...encode(input.substr(unregisteredIndex), dict)
    ];
  };

  console.log({dict, encoded: encode(input, dict)});
});