25 lines
659 B
OCaml
25 lines
659 B
OCaml
let even x = (x land 1) <> 1
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let middle_three_digits x =
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let s = string_of_int (abs x) in
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let n = String.length s in
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if n < 3 then failwith "need >= 3 digits" else
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if even n then failwith "need odd number of digits" else
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String.sub s (n / 2 - 1) 3
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let passing = [123; 12345; 1234567; 987654321; 10001; -10001; -123; -100; 100; -12345]
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let failing = [1; 2; -1; -10; 2002; -2002; 0]
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let print x =
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let res =
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try (middle_three_digits x)
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with Failure e -> "failure: " ^ e
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in
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Printf.printf "%d: %s\n" x res
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let () =
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print_endline "Should pass:";
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List.iter print passing;
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print_endline "Should fail:";
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List.iter print failing;
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;;
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