from itertools import chain, groupby
from random import random
 
maxNumber = 20
 
numbers = [n for n in range(1, maxNumber + 1) if random() < 0.75]
 
def seq2dif(l):
    return [l[0]] + [l[i + 1] - l[i] for i in range(len(l) - 1)]
 
def dif2seq(l):
    c = 0
    s = []
 
    for i in range(len(l)):
        c += l[i]
        s.append(c)
 
    return s
 
def flatten(l):
    return list(chain.from_iterable(l))
 
def encode(l):
    return flatten([[k, len(list(g))] for k, g in groupby(l)])
 
def decode(l):
    return flatten([[l[i * 2]] * l[i * 2 + 1] for i in range(int(len(l) / 2))])
 
print(numbers)
 
compressed = encode(seq2dif(numbers))
print(compressed)
 
print(dif2seq(decode(compressed)))

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