function alternate(s) {
	if (s.length === 1) return 0;
  let charSet = [...new Set(s)];
  let max = 0;
  let occSet = [];
  const isAlternate = (arr) => {
    for (let i = 0; i < arr.length - 1; i++) {
      if (arr[i] === arr[i + 1]) {
        return false;
      }
    }
    return true;
  };

  if (charSet.length === s.length && isAlternate(s)) return s.length;

  for (let i in charSet) {
    for (let j in charSet) {
      if (i === j) continue;
      // saving the combinations that already happened
      let set = charSet[i] + charSet[j];
      let reverse = charSet[j] + charSet[i];
      // If the combination was already analysed, it will pass to the next iteration
      if (occSet.indexOf(set) > 0) continue;

      // Saving the new combination
      occSet.push(set);
      occSet.push(reverse);

      // Removing the 2 combinations from the Set
      let possibiliteis = charSet.filter(
        (v) => !(v === charSet[i] || v === charSet[j])
      );

      let filtered = s;
      for (let p of possibiliteis) {
        // Replace every char excluding the combination
        filtered = filtered.replaceAll(p, '');
      }

      //check if it is max and alternated
      if (filtered.length > max && isAlternate(filtered)) {
        max = filtered.length;
      }
    }
  }

  return max;
}

from itertools import combinations
def alternate(s):
    seen = set()
    for c in s:
        if c not in seen:
            seen.add(c)
    res = 0
    for comb in combinations(seen, r=2):
        s_ = ''.join([c for c in s if c in comb])
        cond = True
        for i in range(len(s_)-1):
            if s_[i] == s_[i+1]:
                cond = False
                break
        if cond:
            res = max(res, len(s_))
    return res

def alternate(s):
    a=list(set(s))
    ans=0
    for x in range(len(a)-1):
        for y in range(1,len(a)-x):
            me=[a[x],a[x+y]]
            nit=""
            for t in s:
                if (t in me):
                    if (nit=="" or t!=nit[-1]):
                        nit+=t
                    else:
                        nit=""
                        break
            if len(nit)>ans:
                ans=len(nit)
    return ans

def alternate(s):
    charSet = list(set(s))
    maxLength = 0
    for i in range(len(charSet) - 1):
        for j in range(i + 1, len(charSet)):
            a, b = charSet[i], charSet[j]
            temp_length = 0
            lastChar = ""
            for letter in s:
                if letter == a:
                    if lastChar == b or lastChar == "":
                        lastChar = a
                        temp_length += 1
                    elif lastChar == a:
                        break 
                if letter == b:
                    if lastChar == a or lastChar == "":
                        lastChar = b
                        temp_length += 1
                    elif lastChar == b:
                        break
            else:
                if maxLength < temp_length:
                    maxLength = temp_length
    return maxLength