check for a pair in power hand

i am trying to check for a pair, I need to compare each value in an array to each other in the array.

the difference will be a multuple of 13. exampe 1 and 14 would be a pair.

if mod (card[ct1]-card[ct2],13) ==0; but not sure how to write it. any help appreciated.

Answer 1

[Rik]

The feasibility of this depends on the size of the arrays involved. If your vectors are too large, the implicit expansion will cause problems.

v1=randi(26,8,1);
v2=randi(26,8,1);
[ind1,ind2]=find(mod(v1-v2.',13)==0);
pairs=[v1(ind1),v2(ind2)]

pairs = 3×2

8 8 21 8 13 26

Answer 2

[Jan]

The trivial approach would be two nested loops:

card   = randi(20, 1, 1000);
result = zeros(2, numel(card));   % Pre-allocate to maximum size
c      = 0;
for i1 = 1:numel(card)
   for i2 = 1:numel(card)
       if mod(card(i1) - card(i2), 13) == 0
           c = c + 1;
           result(1, c) = i1;
           result(2, c) = i2;
       end
   end
end
result = result(:, 1:c);   % Crop unused elements

Rik's vectorized apporach is smarter.