Matrices of words P52233

Using the declarations

    typedef vector<string> Row;
    typedef vector<Row> Matrix;

write a function

    int number_of_words(const Matrix& m, char c, int k);

that returns how many words @w@ of the Matrix @m@ have the character @c@ at the position @k@, that is, fulfil @p[k]@ $=$ @c@ (when @p[k]@ exists). Take into account that the “matrix” @m@ is not necessary rectangular, i.e., some rows may be larger than others.

Precondition

@k@ $\ge 0$

Observation

You only need to submit the required procedure; your main program will be ignored.