题解 | 字符集合

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void (async function () {
  while(line = String(await readline())){
    let arr=[];
    for (let i = 0; i < line.length; i++) {
      if (!arr.includes(line[i])) {
        arr.push(line[i]);
      }
    }
    if(line!='undefined'){
     console.log(arr.join("")); 
    }else{
      break;
    }
  } 
})();