Some suggestions:
function output = scramble(input)
Do not use the term "input" as name of a variable, because this is an important Matlab function.
X = size(input);
Now X is a vector. Better use numel or length.
while X > 0
X does not change its value inside the loop. Therefore the loop will run infinitely.
idx = randi([1 X]);
Keep code as simple as possible. Better:
idx = randi(X);
The purpose of the next two lines is not clear to me:
A(idx) = A(idx) + 1 ;
output = X-1;
Together:
function output = scramble(in)
n = numel(in);
out = repmat(' ', 1, n); % Pre-allocation
while n > 0
idx = randi(n);
out(k) = in(idx);
in(idx) = [];
n = n - 1;
end
The iterative shrinking of the input array is a bad programming pattern and if the input is large (e.g. millions of characters), this will waste time. There are better methods for scrambling, search for "Fisher Yates Shuffle" or "Knuth Shuffle" in the net. This is the algorithm implemente in randperm when called with 2 inputs.
