[38] 外观数列

/**
 * @param {number} n
 * @return {string}
 */
var countAndSay = function (n) {
  if (n === 1) {
    return '1';
  }
  let str = '1';
  while (true) {
    let newStr = '';
    const charArr = str.split('')
    const ll = charArr.length;
    let t = charArr[0];
    let sum = 1;
    for (let i = 1; i < ll; i++) {
      const newt = charArr[i];
      if (newt === t) {
        sum++;
      } else {
        newStr = newStr + String(sum) + t;
        t = newt;
        sum = 1;
      }
    }
    newStr = newStr + String(sum) + t;
    if (n === 2) {
      return newStr;
    } else {
      n = n - 1;
      str = newStr;
    }
  }
};