문자열 압축

const solution = string =>
  string.split('').reduce(
    ({ count, answer }, char, index) => {
      const prevChar = answer[answer.length - 1];
      if (prevChar != char) {
        answer += count == 1 ? char : count + char;
        count = 1;
      } else {
        count++;
        if (index == string.length - 1) answer += count;
      }
      return { count, answer };
    },
    { count: 1, answer: '' },
  ).answer;

const result = solution('KKHSSSKKSSSS');
console.log(result);