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CS 496: Assignment 1

2 Assignment
This assignment is about coding with lists and tuples. The setting is that of a simple
game called Connect the Dots. A coded picture is a list of coordinates such that adjacent
coordinates are aligned. Coordinates must be positive integers. Two coordinates are said to
be aligned if they are either on the same x-axis, the same y-axis, or the difference between
their x and y coordinates is the same (i.e. “diagonal”).
A coded picture induces a picture, namely the one obtained by connecting the coordinates
in the list, in the order they are presented. For example, given the coded picture
[(0,0);(0,4);(2,2);(0,0)]
it induces a triangle.
3 Exercises
We will use the following user defined datatypes for representing coordinates and coded
pictures.
1 type coord = int * int
2 type coded_picture = coord list
1
Below are two examples of coded pictures, the first one determines a box (once the
coordinates are connected) and the second a triangle.
1 let cp1 = [(0 ,0) ;(2 ,0) ;(2 ,2) ;(0 ,2) ;(0 ,0) ]
2 let cp2 = [(0 ,0) ;(4 ,0) ;(4 ,4) ;(0 ,0) ]
3.1 Your Task
Implement the following functions. You should work on the file cp_stub.ml. First rename it
to cp.ml and then start completing the exercises given below.
1. stretch : coded_picture – int – coded-picture
The expression stretch cp factor enlarges the coded picture by a factor of factor in
both axis. For example,
1 utop # stretch cp1 2;;
2 – : coded_pic = [(0 , 0) ; (4 , 0) ; (4 , 4) ; (0 , 4) ; (0 , 0) ]
3 utop # stretch cp2 7;;
4 – : coded_pic = [(0 , 0) ; (28 , 0) ; (28 , 28) ; (0 , 0) ]
Provide two versions:
(a) stretch using explicit recursion; and
(b) stretch_m using map.
2. segment : coord – coord – coord list
Given aligned coordinates c1 and c2, it returns all the intermediate coordinates in the
line segment from c1 to c2, excluding c1 but including c2. For example,
1 # segment (1 ,1) (4 ,4) ;;
2 – : ( int * int ) list = [(2 , 2) ; (3 , 3) ; (4 , 4) ]
3 utop # segment (2 ,2) (5 ,2) ;;
4 – : ( int * int ) list = [(3 , 2) ; (4 , 2) ; (5 , 2) ]
Hint: The predefined function compare: ’a – ’a – int allows you to compare values
as a prefix operation. In particular, compare x 0 behaves like sign.
3. coverage: coded_pic – coord list
1 # coverage cp1 ;;
2 – : coord list =
3 [(0 , 0) ; (1 , 0) ; (2 , 0) ; (2 , 1) ; (2 , 2) ; (1 , 2) ; (0 , 2) ; (0 , 1) ; (0 , 0) ]
4 # coverage cp2 ;;
5 – : coord list =
6 [(0 , 0) ; (1 , 0) ; (2 , 0) ; (3 , 0) ; (4 , 0) ; (4 , 1) ; (4 , 2) ; (4 , 3) ; (4 , 4) ;
7 (3 , 3) ; (2 , 2) ; (1 , 1) ; (0 , 0) ]
Provide two versions:
(a) coverage using explicit recursion; and
2
(b) coverage_f using fold.
4. equivalent_pics : coded_pic – coded_pic – bool
Determines whether two coded pictures are equivalent. Two coded pictures are said
to be equivalent if the coordinates they cover are identical, up to possible duplicates.
For example,
1 utop # equivalent_pics cp1 [(0 ,0) ;(1 ,0) ;(2 ,0) ;(2 ,2) ;(0 ,2) ;(0 ,0) ];;
2 – : bool = true
3 utop # equivalent_pics cp1 [(2 ,2) ;(0 ,2) ;(0 ,0) ;(2 ,0) ;(2 ,2) ];;
4 – : bool = true
5. height : coded_pic – int and width : coded_pic – int
Determines the height (maximum difference between y coordinates) and width of a
picture (maximum difference between x-coordinates). For example,
1 # height cp1 ;;
2 – : int = 2
3 utop # height cp2 ;;
4 – : int = 4
5 utop # width cp2 ;;
6 – : int = 4
7 utop # width cp1 ;;
8 – : int = 2
6. tile : coded_pic – int*int – coded_pic list list
Given a coded picture and a pair of two numbers n and m, it returns a list of list of
pictures. The result is obtained by constructing a first row of n copies, side by side of
the original pictures, and then m rows below that. For example,
1 utop # tile (2 ,3) cp2 ;;
2 – : coded_pic list list =
3 [[[(0 , 0) ; (4 , 0) ; (4 , 4) ; (0 , 0) ]; [(4 , 0) ; (8 , 0) ; (8 , 4) ; (4 , 0) ]];
4 [[(0 , 4) ; (4 , 4) ; (4 , 8) ; (0 , 4) ]; [(4 , 4) ; (8 , 4) ; (8 , 8) ; (4 , 4) ]];
5 [[(0 , 8) ; (4 , 8) ; (4 , 12) ; (0 , 8) ]; [(4 , 8) ; (8 , 8) ; (8 , 12) ; (4 , 8) ]]]
6 utop # tile (2 ,1) cp2 ;;
7 – : coded_pic list list =
8 [[[(0 , 0) ; (4 , 0) ; (4 , 4) ; (0 , 0) ]; [(4 , 0) ; (8 , 0) ; (8 , 4) ; (4 , 0) ]]]
9 utop # tile (2 ,0) cp2 ;;
10 – : coded_pic list list = []
7. tri_aligned: coord – coord – coord – bool
Determines whether three coordinates are aligned, horizontally, vertically or in diagonal. For example,
1 utop # tri_aligned (0 ,0) (4 ,4) (9 ,9) ;;
2 – : bool = true
3 utop # tri_aligned (0 ,0) (0 ,4) (9 ,9) ;;
4 – : bool = false
5 utop # tri_aligned (0 ,0) (0 ,7) (0 ,9) ;;
6 – : bool = true
7 utop # tri_aligned (7 ,7) (2 ,2) (0 ,0) ;;
8 – : bool = true
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8. compress: coded_pic – coded_pic
Compresses a coded picture by eliminating coordinates c2 such that c2 occurs between
two other coordinates c1 and c3 and c1, c2, c3 are aligned. For example,
1 # compress [(0 ,0) ;(1 ,0) ;(2 ,0) ;(2 ,2) ;(0 ,2) ;(0 ,0) ];;
2 – : coded_pic = [(0 , 0) ; (2 , 0) ; (2 , 2) ; (0 , 2) ; (0 , 0) ]
4 Submission instructions
Submit a single file named cp.ml through Canvas. No report is required. Your grade will
be determined as follows:
• You will get 0 points if your code does not compile.
• Partial credit may be given for style, comments and readability.
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