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67 lines
1.5 KiB
Plaintext
67 lines
1.5 KiB
Plaintext
# Implements bitonic sort on a list of numbers encoded as a tree of pairs.
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# https://en.wikipedia.org/wiki/Bitonic_sorter
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# Because we can't know when a tree of pairs is a leaf or a node, we pass the depth everywhere.
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# Generates a tree of pairs with depth 'd' with numbers from 2^d to 0 at the leaves
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def gen(d):
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bend d, x=0:
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when d:
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return (fork(d - 1, x * 2 + 1), fork(d - 1, x * 2))
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else:
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return x
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# Adds all the numbers in a tree of pairs of depth 'd'
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def sum(d, t):
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switch d:
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case 0:
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return t
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case _:
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(t.a, t.b) = t
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return sum(d-1, t.a) + sum(d-1, t.b)
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# Conditionally swaps the values of a pair
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def swap(s, a, b):
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if s:
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return (b,a)
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else:
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return (a,b)
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def warp(d, s, a, b):
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switch d:
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case 0:
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return swap(s + (a > b), a, b)
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case _:
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(a.a,a.b) = a
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(b.a,b.b) = b
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(A.a,A.b) = warp(d-1, s, a.a, b.a)
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(B.a,B.b) = warp(d-1, s, a.b, b.b)
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return ((A.a,B.a),(A.b,B.b))
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def flow(d, s, t):
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switch d:
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case 0:
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return t
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case _:
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(t.a, t.b) = t
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return down(d, s, warp(d-1, s, t.a, t.b))
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def down(d,s,t):
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switch d:
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case 0:
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return t
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case _:
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(t.a, t.b) = t
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return (flow(d-1, s, t.a), flow(d-1, s, t.b))
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# Bitonic sort
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def sort(d, s, t):
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switch d:
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case 0:
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return t
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case _:
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(t.a, t.b) = t
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return flow(d, s, (sort(d-1, 0, t.a), sort(d-1, 1, t.b)))
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def main:
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# Generate a reverse sorted tree of numbers, sort them and then add them up
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return sum(18, sort(18, 0, gen(18))) |