添加两个sparsematrix树图

Question

I'm trying to add two different sparse martices together to achieve one large matrix with all the values from the other matrix. But if they both have a value at a specific key, the values should be added together. What I can't figure out is how to reference the new matrix that is being created so I can put new the new values into it to then return.

Answer 1

I would suggest something like this- note that this is untested code.

public static SparseMatrix add(SparseMatrix a, SparseMatrix b) {
  if (a.rows != b.rows || a.cols != b.cols) {
    // They must be the same dimensions.
    return null;
  }
  return new SparseMatrix(a.rows, a.cols).add(a).add(b);
}

private SparseMatrix add(SparseMatrix a) {
  // Walk all of his.
  for (Integer i : a.matrix.keySet()) {
    // Do I have one of these?
    if (matrix.containsKey(i)) {
      // Yes! Add them together.
      TreeMap<Integer, Double> mine = matrix.get(i);
      TreeMap<Integer, Double> his = a.matrix.get(i);
      // Walk all values in there
      for (Integer j : his.keySet()) {
        // Do I have one of these?
        if (mine.containsKey(j)) {
          // We both have this one - add them.
          mine.put(j, mine.get(j) + his.get(j));
        } else {
          // I do not have this one.
          mine.put(j, his.get(j));
        }
      }
    } else {
      // I do not have any of these - copy them all in.
      matrix.put(i, new TreeMap(a.matrix.get(i)));
    }
  }
  return this;
}