经典面试题：数组去重

  function oSort( arr ) {
                 var result = {};
                 var newArr = [];
                 for (var i = 0 ; i < arr.length; i ++ ) {
                       if (! result[arr[i]]) {
                           newArr.push(arr[i]);
                           result[arr[i]] = 1;
                       }
                }
                 return newArr;
     }

      function oSort2( arr ) {
                 var n = [];
                 for (var i = 0 ; i <arr.length; i ++ ) {
                       if (arr.indexOf(arr[i])== i) {
                           n.push(arr[i]);
                      }
                }
                 return n;
           }

   function oSort3 ( arr ) {
                 var n = [];
                 for (var i = 0 ; i <arr.length; i ++ ) {
                       if (n.indexOf(arr[i])<0 ) {
                           n.push(arr[i]);
                      }
                }
                 return n;
       }