advent_day2a.js

let input = [
 "1-3 a: abcde",
 "1-3 b: cdefg",
 "2-9 c: ccccccccc"
]

// wrong
// function testpassword(line){
//   let [_, lower, upper, char, password] = line.match(/^(\d+)-(\d+)\s(\w):\s(\w+)$/)
//   console.log(line, {lower, upper, char, password})
//   console.log(`${char}{${lower},${upper}}`, new RegExp(`${char}{${lower},${upper}}`).test(password))
//   return new RegExp(`${char}{${lower},${upper}}`).test(password)
// }

function testpassword(line){
  let [_, lower, upper, char, password] = line.match(/^(\d+)-(\d+)\s(\w):\s(\w+)$/)
  let charcount = password.split("").filter(each => each == char).length
  return lower <= charcount && charcount <= upper
}

function testpassword(line){
  let [_, lower, upper, char, password] = line.match(/^(\d+)-(\d+)\s(\w):\s(\w+)$/)
  let lowerchar = password[+lower - 1] == char
  let upperchar = password[+upper - 1] == char
  return lowerchar && !upperchar || upperchar && !lowerchar
}



let valid = input
            .map(testpassword)
            .filter(Boolean)
            .length