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Count contiguous subarrays summing to a target k using a prefix
sum table:
prefix[i+1] = prefix[i] + arr[i]
count = |{ (i, j) : 0 <= i < j <= n, prefix[j] - prefix[i] = k }|
For arr = [1; 1; 1; 2; -1; 3; 1; -2; 4] and k = 3, the seven
witnesses are:
[1, 1, 1] (0..2)
[1, 1, 2, -1] (1..4)
[1, 2] (2..3)
[2, -1, 3, 1, -2] (3..7)
[-1, 3, 1] (4..6)
[3] (5..5)
[1, -2, 4] (6..8)
Negative-valued arrays exercise mixed-sign integer arithmetic.
186 baseline programs total.
17 lines
395 B
OCaml
17 lines
395 B
OCaml
let count_subarr_sum_k arr k =
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let n = Array.length arr in
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let prefix = Array.make (n + 1) 0 in
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for i = 0 to n - 1 do
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prefix.(i + 1) <- prefix.(i) + arr.(i)
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done;
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let count = ref 0 in
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for i = 0 to n - 1 do
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for j = i + 1 to n do
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if prefix.(j) - prefix.(i) = k then count := !count + 1
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done
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done;
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!count
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;;
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count_subarr_sum_k [| 1; 1; 1; 2; -1; 3; 1; -2; 4 |] 3
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