duplicating strings in a cell array

I have a cell array like this:

name = {'aa', 'bb', 'bb','cc','cc','ee','ff','ff','ff'};

I would like to get the indices which are duplicated. Idx = 2,4,7.

I use strcmp and it didn't work.

Answer 1

[madhan ravi]

[~, b, c] = unique(name); 

idx = b(sum(b(c) == unique(b(c)).') > 1)

[madhan ravi]

[~, b, c] = unique(name); 

idx = b(accumarray(c, 1) > 1)