https://twitter.com/loicaroyer/status/1146173537658404864

loicaroyer_closest_integer_product.py

# coding: utf-8
# https://twitter.com/loicaroyer/status/1146173537658404864
#
# #Python Twitter Challenge
# Given a list of integers u=[a_0, ..., a_m]
# find the set of indices {i_0, ..., i_n} for that list such that the product 
# u[i_0]* ... *u[i_n] is the closest to a given integer N.
# The shortest and most #elegant solution wins. 
# (standard libs allowed)
#
# 4:47 PM - 2 Jul 2019

# Mark Kittisopikul, Ph.D.
# July 3rd, 2019
# Northwestern University

import numpy as np
import itertools
from functools import reduce

def find_closest_product_factors(N,u):
    factors = u[u != 1]
    reps = int(np.ceil(np.log(N)//np.log(np.min(factors))))
    combinations = reduce(itertools.chain,
        map(lambda r:itertools.combinations_with_replacement(factors,r+1),
        range(reps)))
    u_i = min(combinations,
        key=lambda c: np.abs(N-np.array(c).prod()))
    i = list(map(lambda ui: np.where(u == ui)[0][0],u_i))
    return i,u_i

u = np.array([2,3,5,9,17])
find_closest_product_factors(72,u)