Permutations of an array

Question

I have an array of integers of length 20, filled with fourteen 0s, two 1s, two 2s and two 3s. It is like this: [0,0,0,3,0,2,0,0,3,0,0,0,1,0,2,0,0,1,0,0].

I need a way to list all of its 20!/(14! 2! 2! 2!) permutations, without repetitions. (Note that in the list there are duplicate elements!)

I'm just looking for the right idea, it isn't necessary that you write the code. But, if you prefer writing the code, I only understand C and Java. Thanks :)

@MichaelT It's not a duplicate! In my array the elements are not all different; the array in the other question has all elements diffent — Matteo, Mar 22 '14 at 17:32
@Matteo You should put emphasis in your question that there are duplicate items in your list and that you don't want duplicate permutations with those. — Euphoric, Mar 22 '14 at 17:35
@Euphoric I thought it was clear from the number 20!/(14! 2! 2! 2!) I put in. But thanks for the suggestion, I'm going to edit the question. — Matteo, Mar 22 '14 at 17:37
This question appears to be off-topic because it is an implementation issue and fails to demonstrate a minimal understanding of the problem to be solved. — , Mar 22 '14 at 23:39
Have a look at: Why was my question down voted? and http://meta.programmers.stackexchange.com/q/6166/ — , Mar 23 '14 at 15:47

score 0 · Accepted Answer · edited May 23 '17 at 12:40

I borrowed algorithm from https://stackoverflow.com/questions/2710713/algorithm-to-generate-all-possible-permutations-of-a-list and made a simple change to it so it ignores same elements when swapping them.

def permute(xs, low=0):
    if low + 1 >= len(xs):
        yield xs
    else:
        for p in permute(xs, low + 1):
            yield p        
        for i in range(low + 1, len(xs)):        
            if xs[low] == xs[i]:
                continue
            xs[low], xs[i] = xs[i], xs[low]
            for p in permute(xs, low + 1):
                yield p        
            xs[low], xs[i] = xs[i], xs[low]

for p in permute([0, 1, 0, 2, 0, 3]):
    print(p)

Can you translate it in C or Java? – Matteo Mar 22 '14 at 19:47 — Matteo, Mar 22 '14 at 19:47

Permutations of an array

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