Python - Index match element Product

Sometimes, while working with Python list we can have a problem in which we have to compare two lists for index similarity and hence can have a task of multiplication equal index pairs. Let’s discuss certain way in which this task can be performed.

Method #1 : Using loop + zip() 
This task can be performed by passing the zip(), which performs task of mapping both list with each other, to the function which computes the product according to equal indices.

# Python3 code to demonstrate working of
# Index match element Product
# using loop + zip()

def prod(val) :     
    res = 1         
    for ele in list(val):         
        res *= ele         
    return res

# initialize lists
test_list1 = [5, 6, 10, 4, 7, 1, 19]
test_list2 = [6, 6, 10, 3, 7, 10, 19]

# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))

# Index match element Product
# using loop + zip()
res = prod(x for x, y in zip(test_list1, test_list2) if x == y)

# printing result
print("Multiplication of Identical elements : " + str(res))

The original list 1 is : [5, 6, 10, 4, 7, 1, 19]
The original list 2 is : [6, 6, 10, 3, 7, 10, 19]
Multiplication of Identical elements : 7980

Time complexity: O(M^N) as the number of combinations generated is M choose N.
Auxiliary space: O(1) constant extra space is required

Method #2 : Using reduce()

import functools
# initialize lists
test_list1 = [5, 6, 10, 4, 7, 1, 19]
test_list2 = [6, 6, 10, 3, 7, 10, 19]
 
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
 
# Index match element Product
# using functools.reduce()
res = 1
res = functools.reduce((lambda x, y: x * y), [x for x, y in zip(test_list1, test_list2) if x == y])
 
# printing result
print("Multiplication of Identical elements : " + str(res))
#This code is contributed by Edula Vinay Kumar Reddy

The original list 1 is : [5, 6, 10, 4, 7, 1, 19]
The original list 2 is : [6, 6, 10, 3, 7, 10, 19]
Multiplication of Identical elements : 7980

Time complexity: o(n)

Space complexity: o(n)