(10%) Given three strings $x[0, ..., n-1]$, $y[0, ..., m-1]$ and $z[0, ..., r-1]$. We say that $z$ is a shuffle of $x$ and $y$ if it contains all characters of $x$ and $y$ and the left-to-right ordering of the characters from $x$ and the characters from $y$ is preserved. For example, "NcCKsiUe" is a shuffle of "NCKU" and "csie". The dynamic programming algorithm uses a table $S$ to check $x$, $y$ and $z$, where $S[i][j]$ is true if and only if the first $i+j$ characters of $z$ are a shuffle of the first $i$ characters of $x$ together with the first $j$ characters of $y$. Complete the following pseudocode for checks whether $z$ is a shuffle of $x$ and $y$ by filling (1), (2) and (3). (please use C-style expression)

isShuffle(x, y, z)
    Let S[0...n][0...m] be a new table
    S[0][0] = true
    if r != n + m
        return false
    for i = 1 to n
        S[i][0] = ____(1) (3%)____
    for j = 1 to m
        S[0][j] = ____(2) (3%)____
    for i = 1 to n
        for j = 1 to m
            S[i][j] = ____(3) (4%)____
    return S[n][m]