根据字符是否重复，将字符串变成()字符组成的字符串

function duplicateEncode(word) {
    word = word.toLocaleUpperCase();
    var strArr = word.split("");
    
    var newStrArr = [];
    for (var i = 0; i < strArr.length; i++) {
        var num = 0;
        for (var j = 0; j < strArr.length; j++) {
            strArr[i] === strArr[j] && num++;
        }
        
        if (num > 1) {
            newStrArr[i] = ")";
        } else {
            newStrArr[i] = "(";
        }
    }
    return newStrArr.join("");
}

// 简洁写法
function duplicateEncode(word){
  return word
    .toLowerCase()
    .split('')
    .map( function (a, i, w) {
      return w.indexOf(a) == w.lastIndexOf(a) ? '(' : ')'
    })
    .join('');
}