Reverse character array using recursion

I'm having trouble creating a function that would reverse a character array using recursion. For example, I want my function to return 'py' when inputting "yp". My overall code doesn't seem right though.

function array2 = charReversal(array1)

if array1==0
    return;
else
    array2=chsrReversal(reverse(array1,array1-1));
    disp(array2)

end

Answer 1

[Guillaume]

I assume this is homework so I'm hesitant even answering the question since the whole purpose of the exercise is to make you think of a recursive algorithm.

It is trivial to reverse a string by recursion: take the first element of the string, put it at the end of the string returned by calling the recursive function with the rest of the string (from character 2 to end). The recursion stops when the function receives only 1 character.

[Todd Wilson]

Yes this is homework, but I am stuck. Your suggestion is a good one to try and I will use it soon. I'm wondering what I should put for "if array1==....."?

[Guillaume]

There is no if array1 == test required. As I wrote, "The recursion stops when the function receives only 1 character". That is what you have to test for.

Answer 2

[Anuj Kumar]

instead of using v=[v(end) reversal(1:end-1)] which won't satisfactorily on large arrays,i would recommend this piece of code

function v=reversal(v)
if(length(v)>1)
d=length(v);
x=0;
if mod(d,2)==0
    x1=d/2;
    x2=x1+1;
    m=v(1:x1);
    n=v(x2:end);
    v=[reversal(n),reversal(m)];
else
    x1=fix(d/2);
    x2=x1+2;
    m=v(1:x1);
    mid=(x1+1:x1+1);
    n=v(x2:end);
    v=[reversal(n),v(mid),reversal(m)];
end
end
end

Answer 3

[Saurabh Wani]

i have try this code and it gives reversal of array elements using recursive method

function w=reversal(v)
s=length(v)
if s==1
    w=v
else
    w=[v(end) reversal(V(1:s-1))]

end

[Hazem Ahmed]

could you explain what are you doing in this line?

w=[v(end) reversal(V(1:s-1))]

[Piyush Gupta]

its an array, you can declare without comma too.

Answer 4

[KSSV]

You can either use fliplr or give indices in reverse.

str = 'py' ;
fliplr(str)
str(end:-1:1)

[Todd Wilson]

I just tried your suggestion of using str(end:-1:1) but I get an error when doing charReversal('ab'):

Undefined function or variable 'str'.

Error in charReversal (line 6) array2=charReversal((str(array1(end:-1:1))));

My code is now:

function [ array2 ] = charReversal( array1 )

if size(array1,2)==1
   array2=1;
else
array2=charReversal((str(array1(end:-1:1))));
end

[KSSV]

Oh dear friend.... str is the string which should be input...in your case it is array1. Your function should be simply:

function array2 = charReversal(array1)
array2=array1(end:-1:1) ;

Save it, it will be saved on the name charReversal.m. To call/ use it:

array2 = charReversal('py') 
array1 = 'matlab' ;
  array2 = charReversal(array1)

[Todd Wilson]

For array2 = charReversal(array1), shouldn't there be a function such as reverse? Also, I need the code to be in recursion.

[KSSV]

Ohh..why recursion needed? That case you may add it. But don't use str.

Answer 5

[ambuj aman]

function out = reversal(in)
    if length(in) <= 1
        out = in;
    else
        out = [ reversal(in(2:end)) in(1) ];
    end
end

Answer 6

[Selman Baysal]

I solve this problem by removing first and last elements in the vector until one or zero element remains.

function w = reversal(v)
if length(v) <= 1
    w = v;
else
    v1 = v(end); v(end) = [];
    v2 = v(1);  v(1) = [];
    w = [v1 reversal(v) v2];
end