Getting permutations of an int[] removing duplicates sets

Question

I have an [] of integers 1<=N<=100 , How can i get permutations of this array? -> Array may contain duplicates, so resulting set of permutations can be duplicate, so

Answer 1

You want all non-duplicate permutations of an array. The number of these, assuming each array entry is unique, Factorial(array.length), quickly becomes uncomputably large. But assuming you want to enumerate them the simplest way is to do the following :

Your problem is basically a selection problem over your alphabet (1 <= N <= 100). It does not matter if you want to select 5 of these or 500, you want to select some number, call it, x. Think of the unique elements you want to select from, those that you do not want to duplicate (this may be a proper subset of your alphabet, or not). Lay these elements out in a row. The length of this row is n. Now the selection problem of enumerating a selection of x of these can be solved as follows. Think of an n bit number, that can only ever contain n-x zeroes. To get this rank-x number, simply start from 0 and enumerate all possible numbers up to 2**n, selecting only those that have exactly x 1s (and n-x zeroes). These 1s then select x positions from the n positions of your alphabet, and each of these rank-x numbers selects a permutation for you.

If anyone knows an optimization so that you don't have to work out all the non-rank-x ones, please say so. EDIT: The answer, it seems, is here