// should be A3b3C1z2n2K1l2Y2i2
    let str = 'AAAbbbCzznnKllYYii'.split('');
    console.log('AAAbbbCzznnKllYYii');
    let scope = '';
    let tmpArr = [];
    str.forEach((element, i) => {
      (function(it) {
        const cur = str[it];
        const prev = str[it-1];
        if(prev) {
          scope = `${scope}${prev}`
          if(prev !== cur) {
            tmpArr = [...tmpArr, `${prev}${scope.length}`]
            scope = ''
          }
          if(it === str.length -1) {
            scope = `${scope}${cur}`
            tmpArr = [...tmpArr, `${prev}${scope.length}`]
          }
        }
      })(i)
    });
    console.log(tmpArr.join(''));