from math import floor
import unittest
################################################################################
# Solution
################################################################################
def bounds(r):
ct = len(r)
if ct % 2 == 0:
h = int(ct / 2)
return ct, h
else:
h = floor(ct / 2)
return ct, h
def find_repeat(xs):
ct, h = bounds(xs)
rl = range(1, h + 1)
rr = range(h + 1, ct)
while True:
nl = len([None for x in xs if x in rl])
nr = len([None for x in xs if x in rr])
branch = rl if nl > nr else rr
if len(branch) == 1:
return branch[0]
ct, h = bounds(branch)
rl = range(branch[0], branch[0])
rr = range(branch[0] + h, branch[-1] + 1)
raise Exception(
'We could not find any duplicates in xs. Perhaps xs did not adhere to the usage contract.'
)
################################################################################
# Tests
################################################################################
class Test(unittest.TestCase):
def test_just_the_repeated_number(self):
actual = find_repeat([1, 1])
expected = 1
self.assertEqual(actual, expected)
def test_short_list(self):
actual = find_repeat([1, 2, 3, 2])
expected = 2
self.assertEqual(actual, expected)
def test_medium_list(self):
actual = find_repeat([1, 2, 5, 5, 5, 5])
expected = 5
self.assertEqual(actual, expected)
def test_long_list(self):
actual = find_repeat([4, 1, 4, 8, 3, 2, 7, 6, 5])
expected = 4
self.assertEqual(actual, expected)
unittest.main(verbosity=2)
