pairwise.py

#python 3

'''
Resources: https://stackoverflow.com/questions/126524/iterate-a-list-with-indexes-in-python
'''

from random import randint
'''
Original pairwise product algorithm
Slowest run time
'''

def max_pairwise_product(numbers):
    n = len(numbers)
    max_product = 0
    for first in range(n):
        for second in range(first + 1, n):
            max_product = max(max_product,
                numbers[first] * numbers[second])

    return max_product

'''
    Faster pairwise product algorithm
    faster runtime
'''


def pairwise1(numbers):

    max_index1 =  0
    max_index2 = 0    
    #find the highest number
    for i, val in enumerate(numbers):
        if int(numbers[i]) > int(numbers[max_index1]):
            max_index1 = i
    
    if max_index1 == 0:
        max_index2 = 1
    else:
        max_index2 = 0   
    #find the second highest number
    for j, val in enumerate(numbers):
        if j!=max_index1 and int(numbers[j]) > int(numbers[max_index2]):
            max_index2 = j
    
        
    
    #print(max_index1)    
    #print(max_index2)
    return int(numbers[max_index1]) * int(numbers[max_index2])    
  


'''
    Another solution to the pairwise product 
    Even faster run time (probably)
'''



def pairwise(arr):
    arr.sort(reverse = True)
    solution = int(arr[0]) * int(arr[1])
    return solution


def stressTest():
   while True:
        arr = []
        for x in range(5):
            random_num = randint(2,101)
            arr.append(random_num)
        print(arr)
        print('####')
        result1 = max_pairwise_product(arr)
        result2 = pairwise1(arr)
        print("Result 1 {}, Result2 {}".format(result1,result2))

        if result1 != result2:
            print("wrong answer: {} **** {}".format(result1, result2))
            break
        else:
            print("############################################# \n Ok", result1, result2)


        




if __name__ == '__main__':
    #stressTest()

    
    length = input()
    numbers = [int(x) for x in input().split()]
    answer = pairwise(numbers)
    answer = pairwise1(numbers)
    print(answer)