Minimum digits to remove to make a number Perfect Square

Given an integer n, we need to find how many digits remove from the number to make it a perfect square.

Examples : 

Input : 8314 
Output: 81 2 
Explanation: If we remove 3 and 4 number becomes 81 which is a perfect square.

Input : 57 
Output : -1

The idea is to generate all possible subsequences and return the optimal string using set bits. Let's suppose we have a string 8314. And using set bits we form all possible subsequences i.e.,
8, 3, 83, 1, 81, 31, 831, 4, 84, 34, 834, 14, 814, 314, 8314.
After forming all possible subsequences, we check which one is the perfect square. And we return a perfect square number that has the minimum length.

In the above example, three perfect squares are 1 4, and 81, so the answer would be 81 because 81 has the max length of 2.  

81 2
-1

Time Complexity: O(n * 2ⁿ)
Auxiliary Space: O(2ⁿ)