http://adventofcode.com/2017

day1.js

const code = document.getElementsByTagName('pre')[0].innerHTML.trim();
let sum = 0;

for(let i=1; i<code.length;i++) {
  const current = code[i],
    prev = code[i-1];

  if(current === prev) { sum += parseInt(current, 10) }
}

if(code[0] === code[code.length-1]) sum += parseInt(code[0], 10)

document.getElementsByTagName('pre')[0].innerHTML = sum;

day2.js

document.getElementsByTagName('pre')[0].innerHTML.trim().split('\n')  
  .map(line => line.split(/\D+/))
  .map(line => Math.max.apply(null, line) - Math.min.apply(null, line))
  .reduce((a, b) => a+b, 0)

day3.js

const steps = n => {
    const root = Math.ceil(Math.sqrt(n)),
          curR = root % 2 !== 0 ? root : root + 1,
          numR = (curR - 1) / 2,
          cycle = n - ((curR - 2) ** 2),
          innerOffset = cycle % (curR - 1);

    return numR + Math.abs(innerOffset - numR);
};

console.log(steps(325489));