Question

Define a function called reverse that takes a string textand returns that string in reverse.

For example: reverse("abcd") should return "dcba".

You may not use reversed or [::-1] to help you with this.
You may get a string containing special characters (for example, !, @, or #).
Above is a problem I saw at codeacademy.com
This is the code dat I wrote. Can any1 tell me what is wrong
def reverse(text):
reversed_string = ""
for i in range(len(text)-1,0):
reversed_string += text[i]
print reversed_string
return reversed_string

reverse("sdgsdfsdf")

Answer 1

What's the output of your code? Are you getting an error?

Answer 2

for i in range(len(text)-1,0):

Should probably have a third argument, the step value, -1.

BTW, recursion will do this nicely.

Answer 3

yes you could probably get some extra credit by using recursion or implementing a LIFO stack

Answer 4

thanks the -1 step worked

Answer 5

Recursive solution:

reverse(xs) =
if (empty(xs))
return nothing
else
return reverse(rest(xs)) + head(xs)

Note:
head(xs) = xs[0]
rest(xs) = xs[1] + xs[2] + ... + xs[size(xs)-1], e.g., in C++: xs.substr(1)

Of course, this is a bad use of recursion. A loop-based solution:

reverse(xs) =
result = nothing
for x in xs
result = x + result
return result

Note how the above simple loop solution is similar to the recursive solution; the "plux x" part is like the "+ head(x)", and the body of the loop is like the "recursive(rest(xs))" part.

A possibly more efficient solution:

reverse(xs) =
size = len(xs)
half = size/2
for i = 0 to half-1
swap(xs[i], size-i-1)

Answer 6

thanks