function findMax(left, right, str) {
  while (str[left] === str[right]) {
    if (!str[left] || !str[right]) {
      break
    }
    left--
    right++
  }
  return right - left - 1
}

function resolve(str) {
  let left = 0
  let right = 0
  let max = 1
  for (let i = 0; i < str.length; i++) {
    left = i
    right = i + 1
    max = Math.max(findMax(left, right, str), max)
    left = i - 1
    right = i + 1
    max = Math.max(findMax(left, right, str), max)
  }
  return max
}

const res = resolve('abac')
console.log(res)