N = 6 # length of numbers to generate
K = 4 # number of bits to be set
 
cur = (1<<K)-1  #smallest number witk K bits set
 
while cur < (1<<N):
 
	print format(cur,'b')
 
	#when you subtract 1, you turn off the lowest 1 bit
	#and set lower bits to 1, so we can get the samallest 1 bit like this:
	lowbit = cur&~(cur-1)
 
	#when you add lowbit, you turn it off, along with all the adjacent 1s
	#This is one more than the number we have to move into lower positions
	ones = cur&~(cur+lowbit)
 
	#cur+lowbit also turns on the first bit after those ones, which
	#is the one we want to turn on, so the only thing left after that
	#is turning on the ones at the lowest positions
	cur = cur+lowbit+(ones/lowbit/2)
 
 

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