advent-dayone.js

const text = await Deno.readTextFile('./day1');

const digits = new Map();
digits.set('zero', '0');
digits.set('one', '1');
digits.set('two', '2');
digits.set('three', '3');
digits.set('four', '4');
digits.set('five', '5');
digits.set('six', '6');
digits.set('seven', '7');
digits.set('eight', '8');
digits.set('nine', '9');

const lines = text.split('\n');
const sum = lines.reduce((acc, line) => {
  // we've gotta pad this because we need to be able to backup to 
  // before our splice if the string starts with a number
  const arr = ['', ...line.split('')];
  let i = 0;
  let firstNum = 0;
  let lastNum = 0;
  let curr = '';
  while (i <= arr.length) {
    const x = arr[i];
    const isNum = Boolean(parseInt(x));
    if (isNum) {
      // if we've got a number but haven't seen one yet set it as the first
      // also set it as the last
      if (firstNum === 0) firstNum = x;
      lastNum = x;
      curr = '';
    } else {
      curr += arr[i];
      // determine if there's a number in our current string
      if (digits.has(curr.substring(0,4))) curr = curr.substring(0,4);
      if (digits.has(curr.substring(1,5))) curr = curr.substring(1,5);
      if (digits.has(curr.substring(0,3))) curr = curr.substring(0,3);
      if (digits.has(curr.substring(1,4))) curr = curr.substring(1,4);
      if (digits.has(curr.substring(2,5))) curr = curr.substring(2,5);
      if (digits.has(curr)) {
        const digit = digits.get(curr);
        const start = Math.max(i - curr.length, 0);
        // splice out the number leaving the last letter
        arr.splice(start, curr.length, digit);
        // back up to before the number we spliced in
        i = start - 1;
        curr = '';
      }
      if (curr.length > 4) {
        curr = curr.substring(1);
      }
    }
    i++;
  }
  return parseInt(firstNum + lastNum) + acc;
}, 0);

console.log(sum);