const SURROGATE_PAIR_RE = /(?:[\ud800-\udbff][\udc00-\udfff])/;
 
function countCodePoints (s) {
  const re = new RegExp(SURROGATE_PAIR_RE.source + "|[\\S\\s]", "g");
  let n = 0;
  while (re.exec(s))
    n++;
  return n;
}
 
function odai_pt15_467 (s) {
  const re = new RegExp("(" + SURROGATE_PAIR_RE.source + "|[\\S\\s])\\1{1,}",
                        "g");
  return s.replace(re, function (substring, character) {
    if (substring.length == 1)
      return substring;
    else
      return character + countCodePoints(substring);
  });
}
 
for (let s of ["あいうえお",
               "ああいいうう",
               "あいうあいう",
               "ああああ",
               "🐤🐤🐤🐤"]) {
  print(odai_pt15_467(s));
}
 

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