Is there a real need of a hashmap for this problem>

  • 1

    I don't think for this problem there is a real need of a hashmap. It is only for pedagogical purpose.
    Creating the hashmap representation of the matrix takes allready O(m*n) time. It is simply sufficient to verify if the elements are 0 before trying to multiply them.

    It is much faster then creating the hashmaps

        int m = A.size();
        int n = B.size();
        int p = B[0].size();
        vector<vector<int>> result(m,vector<int>(p,0));
        for(int i = 0; i < m; i++)
            for(int k = 0; k < n; k++)
                if(A[i][k] != 0)
                    for(int j = 0; j < p; j++)
                        if(B[k][j] != 0)
                            result[i][j] += A[i][k] * B[k][j];
        return result;

  • 0

    For this question it may not, but for general matrix library, hashmap still is a good idea.

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