Created
October 2, 2013 06:39
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# Q3. | |
"1 2 3 4 5 6 [7] 6 5 4 3 2 1 [0] 1 2 [3] 2 1 0 [-1] 0 1 2 3 4 [5] [4] 5 6" | |
def pingpong(n): | |
"""Return the nth element of the ping-pong sequence. | |
>>> pingpong(7) | |
7 | |
>>> pingpong(8) | |
6 | |
>>> pingpong(15) | |
1 | |
>>> pingpong(21) | |
-1 | |
>>> pingpong(22) | |
0 | |
>>> pingpong(30) | |
6 | |
>>> pingpong(68) | |
2 | |
>>> pingpong(69) | |
1 | |
>>> pingpong(70) | |
0 | |
>>> pingpong(71) | |
1 | |
>>> pingpong(72) | |
0 | |
>>> pingpong(100) | |
2 | |
""" | |
"*** YOUR CODE HERE ***" | |
def pingpongdir(n, direction): | |
if n == 1: | |
return 1 | |
elif direction: | |
if has_seven(n) or n % 7 == 0: | |
return pingpongdir(n-1, False) + 1 | |
else: | |
return pingpongdir(n-1, True) + 1 | |
else: | |
if has_seven(n) or n % 7 == 0: | |
return pingpongdir(n-1, True) - 1 | |
else: | |
return pingpongdir(n-1, False) - 1 | |
return pingpongdir(n, False) | |
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def has_seven(k):
"""Has a has_seven
>>> has_seven(3)
False
>>> has_seven(7)
True
>>> has_seven(2734)
True
>>> has_seven(2634)
False
>>> has_seven(734)
True
>>> has_seven(7777)
True
"""
"*** YOUR CODE HERE ***"
if k % 10 == 7:
return True
elif k // 10 == 0:
return False
else:
return has_seven(k // 10)