Reduction

Answer

O(n^2) time:

function StringReduction(str) {
  flag = true;
  while (flag) {
    flag = false;
    for (let i = 1; i < str.length; i++) {
      if (/ab|ba/i.test(`${str[i - 1]}${str[i]}`)) {
        str = str.replace(/ab|ba/i, 'c');
        flag = true;
      } else if (/bc|cb/i.test(`${str[i - 1]}${str[i]}`)) {
        str = str.replace(/bc|cb/i, 'a');
        flag = true;
      } else if (/ac|ca/i.test(`${str[i - 1]}${str[i]}`)) {
        str = str.replace(/ac|ca/i, 'b');
        flag = true;
      }
    }
  }
  return str.length;
}
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O(n) time:

function StringReduction(str) {
  flag = true;
  while (flag) {
    flag = false;
    if (/ab|ba|ab|ba|ac|ca/i.test(str)) {
      str = str.replace(/ab|ba/i, 'c');
      str = str.replace(/bc|cb/i, 'a');
      str = str.replace(/ac|ca/i, 'b');
      flag = true;
    }
  }
  return str.length;
}
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