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August 29, 2020 10:26
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from functools import reduce | |
def naive(ar, length): | |
# Наивное решение полным перебором. Сложность - O(n**2). | |
# Проверяем все возможные подмассивы в массиве. | |
# Уверен, что не пройдет по быстродействию. | |
if 0 == length: | |
return 0 | |
if 1 == length: | |
return 1 if ar[0] else 0 | |
result = 0 | |
for i in range(length - 1): | |
s = ar[i] | |
for j in range(i + 1, length): | |
s = s ^ ar[j] | |
if s: | |
result = max(result, j - i + 1) | |
return result | |
def task(ar, length): | |
# Если последовательность пуста, ответ - 0 | |
if 0 == length: | |
return 0 | |
# Если массив состоит из одних нулей, ответ - 0 | |
if all(elem == 0 for elem in ar): | |
return 0 | |
# Если xor-сумма всего массива ненулевая, ответ - весь массив | |
if 0 != reduce(lambda x,y: x^y, ar, 0): | |
return length | |
# Иначе ищем первый и последний ненулевые элементы | |
first = 0 | |
for i in range(length): | |
if ar[i]: | |
first = i | |
break | |
last = length - 1 | |
for i in range(length - 1, -1, -1): | |
if ar[i]: | |
last = i | |
break | |
# Возвращаем длину подмассива, отрезав часть с той стороны, с которой меньше нулей | |
return length - min(first, length - last - 1) - 1 | |
# Набор тестов | |
ar = [] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0, 1] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0, 0, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0, 1, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1, 0, 1] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [0, 0, 3, 7, 4, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1, 0, 0, 3, 7, 4, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1, 0, 0, 3, 7, 4, 0, 1] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) | |
ar = [1, 2, 3, 4, 5, 6, 7, 8, 9, 0] | |
assert(naive(ar, len(ar)) == task(ar, len(ar))) |
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