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var reformat = function (s) {
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  let letter = [],
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    digit = [];
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  for (let i = 0; i < s.length; i++) {
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    s[i] >= 0 && s[i] <= 9 ? digit.push(s[i]) : letter.push(s[i]);
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  }
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  // impossible to reformat
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  if (Math.abs(letter.length - digit.length) >= 2) {
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    return "";
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  }
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  let i = 0,
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    output = "";
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  while (i < letter.length && i < digit.length) {
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    output = output + letter[i] + digit[i];
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    i++;
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  }
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  if (i < letter.length) {
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    output = output + letter[i];
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  } // add in the END
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  if (i < digit.length) {
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    output = digit[i] + output;
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  } // add in the FRONT
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  return output;
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};