slow.py

# Возвращаем элементы первого массива, которые есть во втором
import random
import time

def intersection_with_loops(first_array, second_array):
  result = []
  for first_element in first_array:
    if first_element in second_array:
      result.append(first_element)
  return result

def intersection_with_dicts(first_array, second_array):
  result = []
  second_dict = {k: True for k in second_array}
  for first_element in first_array:
    if first_element in second_dict:
      result.append(first_element)
  return result

first_array = [random.randint(0, 100000) for _ in range(50000)]
second_array = [random.randint(0, 100000) for _ in range(50000)]

start_time = time.time()
intersection_with_loops(first_array, second_array)
first_completed_time = time.time()
print("Loop in loop completed in %.f seconds" % (first_completed_time - start_time))
intersection_with_dicts(first_array, second_array)
second_completed_time = time.time()
print("Dict + loop completed in %.f seconds" % (second_completed_time - first_completed_time))
# Loop in loop completed in 32 seconds
# Dict + loop completed in 0 seconds

start_time = time.time()
set(first_array).intersection(set(second_array))
first_completed_time = time.time()
print("Loop in loop completed in %.f seconds" % (first_completed_time - start_time))
Loop in loop completed in 0 seconds