Question

I’d appreciate any help on the following problem. I have n integers from 0 to n-1, and I’m trying to generate a list of all possible combinations of length k (i.e. k concatenated integers) such that every pair of consecutive integers are not equal. So, for example, (1)(2)(3)(2) would be valid with k = 4, but (1)(2)(3)(3) would not be valid. Any ideas on how to approach this most efficiently? (I don’t care much about length/degree of complexity of the code, just efficiency)

Answer 1

It is the code:

    void Generate(int[] source, List<int[]> result, int[] build, int k, int num) {
      if (num == k) {
        int[] a = (int[])build.clone();
        result.add(a);
        return;
      }

      for (int i = 0; i < source.length; i++)
        if (num == 0 || source[i] != build[num - 1])
        {
          build[num] = source[i];
          Generate(source, result, build, k, num + 1);
        }
    }

How to call:

    int k = 2;
    List<int[]> a = new ArrayList<int[]>();
    Generate(new int[]{1,2,3}, a, new int[k], k, 0);