Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given an array target of n integers. From a starting array arr consisting of n 1's, you may perform the following procedure :

let x be the sum of all elements currently in your array.
choose index i, such that 0 <= i < n and set the value of arr at index i to x.
You may repeat this procedure as many times as needed.

Return true if it is possible to construct the target array from arr, otherwise, return false.
 
Please complete the following python code precisely:
```python
class Solution:
    def isPossible(self, target: List[int]) -> bool:
```