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# Given a string, return the same string, reversed.

# can't use .reverse()

def rev_str(string):

"""

>>> rev_str('hello')

'olleh'

>>> rev_str('1234h')

'h4321'

>>> rev_str('')

''

"""

# Runtime: O(n)

reversed_str = ""

list_str = list(string)

# ['h', 'e', l, l, o]

for l in range(len(list_str)):

letter = list_str.pop()

# l

reversed_str += letter

# oll

return reversed_str

def rev_str_2(string):

"""

>>> rev_str_2('hello')

'olleh'

>>> rev_str_2('1234h')

'h4321'

>>> rev_str_2('')

''

"""

# Runtime: O(n)

return string[::-1]

def rev_str_3(string):

"""

>>> rev_str_3('hello')

'olleh'

>>> rev_str_3('1234h')

'h4321'

>>> rev_str_3('')

''

"""

# Runtime: O(n)

if len(string) == 0:

return string

return string[-1] + rev_str_3(string[:-1])

if __name__ == '__main__':

import doctest

results = doctest.testmod()

if results.failed == 0:

print "ALL TESTS PASSED!"