import itertools
from collections import Counter
#permutations
print(list(map("".join, itertools.permutations('hello'))))
#n most common elements in arr and num occurences
arr = [1, 3, 4, 1, 2, 1, 1, 3, 4, 3, 5, 1, 2, 5, 3, 4, 5]
counter = Counter(arr)
top_three = counter.most_common(3)
#string at [::-1] is reverse