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5.00-even_odd_array.py
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5.00-even_odd_array.py
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import collections
import functools
from typing import List
from test_framework import generic_test
from test_framework.test_failure import TestFailure
from test_framework.test_utils import enable_executor_hook
def is_even(x):
return x % 2 == 0
def is_odd(x):
return x % 2 == 1
def even_odd_self(A: List[int]) -> None:
n = len(A)
i, j = 0, -1
while i <= j % n:
if is_even(A[i]):
i += 1
else:
while abs(j) < n and is_odd(A[j]):
j -= 1
else:
if i >= j % n:
break
A[i], A[j] = A[j], A[i]
i += 1
j -= 1
# NOTE: the key difference b/w the book vs. our soln is that the book's soln
# doesn't care to avoid swapping an odd at the beginning w/ another odd near
# the end; as such swaps will decrement the end-odd pointer anyway, so
# eventually an even near the end will be reached and get swapped with the
# same-indexed odd number near the beginning
def even_odd_book(A: List[int]) -> None:
next_even, next_odd = 0, len(A) - 1
while next_even < next_odd:
if A[next_even] % 2 == 0:
next_even += 1
else:
A[next_even], A[next_odd] = A[next_odd], A[next_even]
next_odd -= 1
@enable_executor_hook
def even_odd_wrapper(executor, A):
before = collections.Counter(A)
# executor.run(functools.partial(even_odd_self, A))
executor.run(functools.partial(even_odd_book, A))
in_odd = False
for a in A:
if a % 2 == 0:
if in_odd:
raise TestFailure('Even elements appear in odd part')
else:
in_odd = True
after = collections.Counter(A)
if before != after:
raise TestFailure('Elements mismatch')
if __name__ == '__main__':
exit(
generic_test.generic_test_main('even_odd_array.py',
'even_odd_array.tsv', even_odd_wrapper))