An old contest question.

Taken from this forum post--
http://compsci.ca/v3/viewtopic.php?t=2192

The question

A spiral of numbers can start and end with any positive integers less than 100. Write a program which will accept two positive integers x and y as input, and output a list of numbers from x to y inclusive, shown in a spiral. You may assume that the end value is greater than or equal to the start value.


A spiral starts with the first number in the centre. The next number appears immediately below the first number. The spiral continues with the numbers increasing in a counter-clockwise direction until the last number is printed. Read the input from the keyboard and display the output on the screen.

Sample session:

Start value:
10
End value:
27
27 26
16 15 14 25
17 10 13 24
18 11 12 23
19 20 21 22


Start value:
10
End value:
12


12 11
7 10
8 9

In Object-Oriented Turing, the solution:

var start, finish, r, c, counter, i, rchange, cchange : int
get start, finish
r := 13
c := 40
counter := 1
i := start
rchange := 1
cchange := 4
loop
exit when i >= finish
for j : 1 .. counter
locate (r, c)
if i < 10 then put " ", i .. else put i .. end if exit when i >= finish
i += 1
r += rchange
end for
for j : 1 .. counter
locate (r, c)
if i < 10 then put " ", i .. else put i .. end if exit when i >= finish
i += 1
c += cchange
end for
rchange *= -1
cchange *= -1
counter += 1
end loop