Given a string containing brackets []
, braces {}
, parentheses ()
,
or any combination thereof, verify that any and all pairs are matched
and nested correctly.
For library documentation, follow Useful OCaml resources.
A Makefile
is provided with a default target to compile your solution and run the tests. At the command line, type:
make
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Ginna Baker
open Base
open OUnit2
open Matching_brackets
let ae exp got _test_ctxt =
assert_equal exp got ~printer:Bool.to_string
let tests = [
"paired square brackets" >::
ae true (are_balanced "[]");
"empty string" >::
ae true (are_balanced "");
"unpaired brackets" >::
ae false (are_balanced "[[");
"wrong ordered brackets" >::
ae false (are_balanced "}{");
"wrong closing bracket" >::
ae false (are_balanced "{]");
"paired with whitespace" >::
ae true (are_balanced "{ }");
"partially paired brackets" >::
ae false (are_balanced "{[])");
"simple nested brackets" >::
ae true (are_balanced "{[]}");
"several paired brackets" >::
ae true (are_balanced "{}[]");
"paired and nested brackets" >::
ae true (are_balanced "([{}({}[])])");
"unopened closing brackets" >::
ae false (are_balanced "{[)][]}");
"unpaired and nested brackets" >::
ae false (are_balanced "([{])");
"paired and wrong nested brackets" >::
ae false (are_balanced "[({]})");
"paired and incomplete brackets" >::
ae false (are_balanced "{}[");
"too many closing brackets" >::
ae false (are_balanced "[]]");
"math expression" >::
ae true (are_balanced "(((185 + 223.85) * 15) - 543)/2");
"complex latex expression" >::
ae true (are_balanced "\\left(\\begin{array}{cc} \\frac{1}{3} & x\\\\ \\mathrm{e}^{x} &... x^2 \\end{array}\\right)");
]
let () =
run_test_tt_main ("matching-brackets tests" >::: tests)
open Base
;;
let try_pop_char stack c =
match Stack.pop stack with
| Some c' when Char.(c' = c) -> Some c
| Some c' -> Stack.push stack c'; None
| _ -> None
;;
let lex_brackets s =
let consume_tokens stack s =
String.foldi ~init:(Ok s) ~f:(fun i acc c ->
let map_pop_error = function
| Some _ -> acc
| None -> Error(i, c)
in
if Result.is_error acc then acc else
match c with
| '(' | '{' | '[' -> Stack.push stack c; acc
| ')' -> try_pop_char stack '(' |> map_pop_error
| '}' -> try_pop_char stack '{' |> map_pop_error
| ']' -> try_pop_char stack '[' |> map_pop_error
| _ -> acc
) s
in
let symbols = Stack.create () in
Result.(consume_tokens symbols s >>= (fun s' -> match Stack.top symbols with
| Some s -> Error(0, s)
| None -> Ok s'))
;;
let are_balanced s = Result.is_ok (lex_brackets s)
;;
Starting the solution by drawing a state machine for it helped keep the strategy clear in my head. I suspect this solution can be made simpler, but I've moved on from it.
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