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to Rectangles in the OCaml Track

Published at Mar 16 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Count the rectangles in an ASCII diagram like the one below.

   +--+
  ++  |
+-++--+
|  |  |
+--+--+

The above diagram contains 6 rectangles:



+-----+
|     |
+-----+
   +--+
   |  |
   |  |
   |  |
   +--+
   +--+
   |  |
   +--+




   +--+
   |  |
   +--+


+--+
|  |
+--+

  ++
  ++


You may assume that the input is always a proper rectangle (i.e. the length of every line equals the length of the first line).

Getting Started

For installation and learning resources, refer to the exercism help page.

Installation

To work on the exercises, you will need Opam and Base. Consult opam website for instructions on how to install opam for your OS. Once opam is installed open a terminal window and run the following command to install base:

opam install base

To run the tests you will need OUnit. Install it using opam:

opam install ounit

Running Tests

A Makefile is provided with a default target to compile your solution and run the tests. At the command line, type:

make

Interactive Shell

utop is a command line program which allows you to run Ocaml code interactively. The easiest way to install it is via opam:

opam install utop

Consult utop for more detail.

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If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

test.ml

open OUnit2
open Rectangles

let ae exp got _test_ctxt = assert_equal exp got ~printer:string_of_int

let tests = [
   "no rows" >::
      ae 0 (count_rectangles [||]);
   "no columns" >::
      ae 0 (count_rectangles [|""|]);
   "no rectangles" >::
      ae 0 (count_rectangles [|" "|]);
   "one rectangle" >::
      ae 1 (count_rectangles [|"+-+"; 
                               "| |"; 
                               "+-+"|]);
   "two rectangles without shared parts" >::
      ae 2 (count_rectangles [|"  +-+"; 
                               "  | |"; 
                               "+-+-+"; 
                               "| |  "; 
                               "+-+  "|]);
   "five rectangles with shared parts" >::
      ae 5 (count_rectangles [|"  +-+"; 
                               "  | |"; 
                               "+-+-+"; 
                               "| | |"; 
                               "+-+-+"|]);
   "rectangle of height 1 is counted" >::
      ae 1 (count_rectangles [|"+--+"; 
                               "+--+"|]);
   "rectangle of width 1 is counted" >::
      ae 1 (count_rectangles [|"++"; 
                               "||"; 
                               "++"|]);
   "1x1 square is counted" >::
      ae 1 (count_rectangles [|"++";
                               "++"|]);
   "only complete rectangles are counted" >::
      ae 1 (count_rectangles [|"  +-+"; 
                               "    |"; 
                               "+-+-+"; 
                               "| | -"; 
                               "+-+-+"|]);
   "rectangles can be of different sizes" >::
      ae 3 (count_rectangles [|"+------+----+"; 
                               "|      |    |"; 
                               "+---+--+    |"; 
                               "|   |       |"; 
                               "+---+-------+"|]);
   "corner is required for a rectangle to be complete" >::
      ae 2 (count_rectangles [|"+------+----+"; 
                               "|      |    |"; 
                               "+------+    |"; 
                               "|   |       |"; 
                               "+---+-------+"|]);
   "large input with many rectangles" >::
      ae 60 (count_rectangles [|"+---+--+----+"; 
                                "|   +--+----+"; 
                                "+---+--+    |"; 
                                "|   +--+----+"; 
                                "+---+--+--+-+"; 
                                "+---+--+--+-+"; 
                                "+------+  | |"; 
                                "          +-+"|]);
]

let () =
  run_test_tt_main ("rectangles tests" >::: tests)
open Base

let is_vertice c = Char.(c = '+')

let is_h_edge c = Char.(c = '-' || is_vertice c)

let is_v_edge c = Char.(c = '|' || is_vertice c)

let is_rectangle diagram r c r' c' =
  let range = Sequence.range
      ~start:`exclusive
      ~stop:`exclusive in
  is_vertice diagram.(r).[c'] &&
  is_vertice diagram.(r').[c] &&
  (range c c'
   |> Sequence.for_all
     ~f:(fun i ->
         is_h_edge diagram.(r).[i] &&
         is_h_edge diagram.(r').[i]
       )
  ) &&
  (range r r'
   |> Sequence.for_all
     ~f:(fun i ->
         is_v_edge diagram.(i).[c] &&
         is_v_edge diagram.(i).[c']
       )
  )

let count_rectangles diagram =
  let height = Array.length diagram in
  let width = String.length diagram.(0) in
  let count = ref 0 in
  for r = 0 to height - 2 do
    for c = 0 to width - 2 do
      if is_vertice diagram.(r).[c]
      then
        for r' = r + 1 to height - 1 do
          for c' = c + 1 to width - 1 do
            if is_vertice diagram.(r').[c'] &&
               is_rectangle diagram r c r' c'
            then
              Int.incr count
          done
        done
    done
  done;
  !count

let count_rectangles diagram =
  if Array.length diagram < 2 ||
     String.length diagram.(0) < 2
  then 0
  else count_rectangles diagram

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