Here's a an iterator to generate combinations.
iterator choose*[T](a: openarray[T], num_choose: int): seq[T] =
var
chosen: seq[T]
i = 0
i_stack = newSeqOfCap[int](num_choose)
while true:
if chosen.len == num_choose:
yield chosen
discard chosen.pop()
i = i_stack.pop() + 1
elif i != a.len:
chosen.add(a[i])
i_stack.add(i)
inc i
elif i_stack.len > 0:
discard chosen.pop()
i = i_stack.pop() + 1
else:
break
Run
Example use:
for choice in choose(@[11, 22, 33, 44, 55, 66], 3):
echo choice
Run
Outputs:
@[11, 22, 33]
@[11, 22, 44]
@[11, 22, 55]
@[11, 22, 66]
@[11, 33, 44]
@[11, 33, 55]
@[11, 33, 66]
@[11, 44, 55]
@[11, 44, 66]
@[11, 55, 66]
@[22, 33, 44]
@[22, 33, 55]
@[22, 33, 66]
@[22, 44, 55]
@[22, 44, 66]
@[22, 55, 66]
@[33, 44, 55]
@[33, 44, 66]
@[33, 55, 66]
@[44, 55, 66]
Run
