题目

传入一个字符串，返回一个新的字符串。如果旧字符串中字符只出现了一次，则返回'('，反之，则返回')'。忽略大小写。

The goal of this exercise is to convert a string to a new string where each character in the new string is '(' if >that character appears only once in the original string, or ')' if that character appears more than once in the >original string. Ignore capitalization when determining if a character is a duplicate.

Examples:

"din" => "((("

"recede" => "()()()"

"Success" => ")())())"

"(( @" => "))(("

我的

function duplicateEncode(word){
    const newWord = word.toLowerCase();
    let box = [];
    for(i=0; i<newWord.length; i++){
        let idx = newWord.indexOf(newWord[i]);
        if (newWord.indexOf(newWord[i], idx + 1) > 0) { //whether duplicated with lateral
            box.push(')');
        } else if(newWord.indexOf(newWord[i]) < i) { //whether duplicated with before
            box.push(')');
        } else {
            box.push('(');
        }
    }
    return box.join('');
}

别人的

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

感想

想到了indexOf，却没有想到lastIndexOf，妙妙妙