# A non-empty array A consisting of N integers is given. The consecutive elements of array A represent consecutive cars on a road.

# Array A contains only 0s and/or 1s:

# 0 represents a car traveling east,
# 1 represents a car traveling west.
# The goal is to count passing cars. We say that a pair of cars (P, Q), where 0 ≤ P < Q < N, is passing when P is traveling to the east and Q is traveling to the west.

# For example, consider array A such that:

#   A[0] = 0
#   A[1] = 1
#   A[2] = 0
#   A[3] = 1
#   A[4] = 1
# We have five pairs of passing cars: (0, 1), (0, 3), (0, 4), (2, 3), (2, 4).

# Write a function:

# def solution(A)

# that, given a non-empty array A of N integers, returns the number of pairs of passing cars.

# The function should return −1 if the number of pairs of passing cars exceeds 1,000,000,000.

# For example, given:

#   A[0] = 0
#   A[1] = 1
#   A[2] = 0
#   A[3] = 1
#   A[4] = 1
# the function should return 5, as explained above.

# Write an efficient algorithm for the following assumptions:

# N is an integer within the range [1..100,000];
# each element of array A is an integer that can have one of the following values: 0, 1.


import numpy as np
import unittest


def solution(array):
    cars_passing = 0
    count = 0
    for car in array:
        if car == 0 :
            cars_passing += 1
        elif car == 1 :
            count += cars_passing
            if count > 1000000000 : 
                return -1
    return count

#the solution for codelity is intend to use suffix sum
def codility_solution(A):
    suffix_sum = [0] * (len(A) + 1)
    for i in range(len(A) -1, -1, -1):
        suffix_sum[i] = A[i]+ suffix_sum[i+1]
    
    count = 0
    for i in range(len(A)):
        if A[i] == 0:
            coutn += suffix_sum[i]
        if count > 1000000000:
            return -1
    return count

class TestSolution(unittest.TestCase):

    def test1(self):
        cars = np.array([0,1,0,1,1])
        res = solution(cars)
        expected = 5
        self.assertEqual(res, expected, "Should be 5")

if __name__ == "__main__":
    unittest.main()

        