Minimum penalty for a shop

We will count the number of penaly and then iterate over the customers, canculate the minimum penalty for each customer and add it to the total penalty.

class Solution:
    def bestClosingTime(self, customers: str) -> int:
        n = len(customers)
        penalty = customers.count('Y')

        if penalty == n: 
            return n

        minPenalty, res = n, 0
        for idx, value in enumerate(customers):
            if minPenalty > penalty:
                minPenalty = penalty
                res = idx
            if value == 'Y':
                penalty -= 1
            else:
                penalty += 1

        if minPenalty > penalty: 
            return n

        return res

Time complexity: O(n)
Space complexity: O(1)