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C++-style lower_bound / upper_bound on a sorted array:
lower_bound — first index >= x (loop uses arr.(mid) < x)
upper_bound — first index > x (loop uses arr.(mid) <= x)
a = [|1; 2; 2; 3; 3; 3; 5; 7; 9|]
upper(x) - lower(x) gives the count of x in a:
cnt3 = 3 cnt2 = 2 cnt5 = 1 cnt9 = 1 cnt4 = 0
fingerprint = 3*1000 + 2*100 + 1*10 + 1 + 0 = 3211
Tests parallel while loops with bisection on ref, mixed strict
and non-strict comparison branches, count-via-subtraction idiom.
176 baseline programs total.
28 lines
747 B
OCaml
28 lines
747 B
OCaml
let lower_bound arr x =
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let lo = ref 0 and hi = ref (Array.length arr) in
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while !lo < !hi do
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let mid = (!lo + !hi) / 2 in
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if arr.(mid) < x then lo := mid + 1
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else hi := mid
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done;
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!lo
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let upper_bound arr x =
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let lo = ref 0 and hi = ref (Array.length arr) in
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while !lo < !hi do
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let mid = (!lo + !hi) / 2 in
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if arr.(mid) <= x then lo := mid + 1
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else hi := mid
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done;
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!lo
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;;
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let a = [| 1; 2; 2; 3; 3; 3; 5; 7; 9 |] in
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let cnt3 = upper_bound a 3 - lower_bound a 3 in
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let cnt2 = upper_bound a 2 - lower_bound a 2 in
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let cnt5 = upper_bound a 5 - lower_bound a 5 in
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let cnt9 = upper_bound a 9 - lower_bound a 9 in
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let cnt4 = upper_bound a 4 - lower_bound a 4 in
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cnt3 * 1000 + cnt2 * 100 + cnt5 * 10 + cnt9 + cnt4
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