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Python Program for Find remainder of array multiplication divided by n

  • Difficulty Level : Easy
  • Last Updated : 07 Sep, 2021

Given multiple numbers and a number n, the task is to print the remainder after multiply all the number divide by n.
Examples: 

Input : arr[] = {100, 10, 5, 25, 35, 14}, 
            n = 11
Output : 9
100 x 10 x 5 x 25 x 35 x 14 = 61250000 % 11 = 9

Naive approach: First multiple all the numbers then take % by n then find the remainder, But in this approach, if the number is maximum of 2^64 then it gives the wrong answer.
Approach that avoids overflow : First take a remainder or individual number like arr[i] % n. Then multiply the remainder with the current result. After multiplication, again take the remainder to avoid overflow. This works because of the distributive properties of modular arithmetic. ( a * b) % c = ( ( a % c ) * ( b % c ) ) % c 

#to use reduce function import reduce from functools

from functools import reduce

def find_remainder(arr,n):

#use the reduce function to calculate sum

   sum_1=reduce(lambda x,y: x*y,arr)

   remainder=sum_1%n

   print(remainder)

arr=[100,10,5,25,35,14]

n=11

find_remainder(arr,n)

Output: 

9

Please refer complete article on Find remainder of array multiplication divided by n for more details! 

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