451. 根据字符出现频率排序

 1/**
 2 * @param {string} s
 3 * @return {string}
 4 */
 5var frequencySort = function(s) {
 6    const record = {};
 7    const sArr = [...s];
 8    sArr.forEach(value => {
 9        record[value] = (record[value] || 0) + 1;
10    });
11
12    // a 出现的次数大于 b
13    return sArr.sort((a, b) => record[a] === record[b] ?
14        a.charCodeAt(0) - b.charCodeAt(0) : record[b] - record[a]
15    ).join('');
16};
17
18ensureEqual(frequencySort("tree"), "eert", 'test 1');
19ensureEqual(frequencySort("trreee"), "eeerrt", 'test 2');
20ensureEqual(frequencySort("abaccadeeefaafcc"), "aaaaacccceeeffbd", 'test 3');
21ensureEqual(frequencySort("loveleetcode"), "eeeelloocdtv", 'test 4');