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faizan2700 2019-12-17 22:48:50 +05:30
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dynamic_programming/iterating_through_submasks.py
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'''
You are given a bitmask m and you want to efficiently iterate through all of
its submasks. The mask s is submask of m if only bits that were included in
bitmask are set
'''
def list_of_submasks(mask)->list:
"""
Args:
mask : number which shows mask ( always integer > 0, zero does not have any submasks )
Returns:
all_submasks : the list of submasks of mask (mask s is called submask of mask
m if only bits that were included in original mask are set
Raises:
AssertionError: mask not positive integer
>>> list_of_submasks(15)
[15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> list_of_submasks(13)
[13, 12, 9, 8, 5, 4, 1]
"""
fmt = "n needs to be positive integer, your input {}"
assert isinstance(mask, int) and mask > 0, fmt.format(mask)
'''
first submask iterated will be mask itself then operation will be performed
to get other submasks till we reach empty submask that is zero ( zero is not
included in final submasks list )
'''
all_submasks = []
submask = mask
while submask:
all_submasks.append(submask)
submask = (submask-1) & mask
return all_submasks
if __name__ == '__main__':
import doctest
doctest.testmod()