数组中找到相同的数据和其下标（有可能多组重复的数据）

 	   let arr = [1,2,3,1,2,3,2,1,3,4,4,5]
       const nary = arr.reduce((total, item, index) => {
          if (total[item]) total[item].push(index);
          else total[item] = [index];
          if (index === arr.length - 1)
            Object.keys(total).map((key) => {
              return total[key].length <= 1 && delete total[key];
            });
          return total;
       }, {});
       console.log(nary)  
       //打印出的结果
       {
        1:[0,3,7],
        2:[1,4,6],
        3:[2,5,8],
        4:[9:10]
       }