Skating shortest path

int dx[] = { 1, 0, -1,  0 };      // The directions in which Susy can skate.
int dy[] = { 0, 1,  0, -1 };

int sum = 0;
for (int rink = 0; rink < 5; rink++) {
    int spath[][] = new int[22][22];                // We use a rink of 22x22, because we add a wall around it.

// spath[x][y] = -2 for a wall; -1 for a freely accessible position;
// and spath[x][y] = n >= 0 means that Susy can get there and stop there in n steps.

    boolean isnew[][] = new boolean[22][22];    // Which positions must we consider for further investigation?

    int sx = 0, sy = 0; 

    for (int x = 0; x < 22; x++) for (int y = 0; y < 22; y++) {   // First make everything a "wall".
            spath[x][y] = -2;
            isnew[x][y] = false;
    }

    for (int x = 1; x <= 20; x++) for (int y = 1; y <= 20; y++) {  // Copy the shape of the rink.
        char c = rinks[rink][y-1].charAt(x-1);

        if (c == '.' || c == 'D') spath[x][y] = -1;
        if (c == 'S') { spath[x][y] = 0; isnew[x][y] = true; }  // starting point
        if (c == 'D') { sx = x; sy = y; }   // (sx, sy) = Daddy's position
    }

    boolean changed = true;
    while (changed) {
        changed = false;   // We keep going until nothing changes.

        for (int x = 1; x <= 20; x++) for (int y = 1; y <= 20; y++)
            if (isnew[x][y]) {
                isnew[x][y] = false;   // Start at the positions marked as "new".

                for (int d = 0; d < 4; d++) {   // Skate in each direction ...
                    int xx = x, yy = y;

                    int l = 0;
                    while (spath[xx][yy] > -2) {     // ... until Susy hits a wall.
                        xx += dx[d]; yy += dy[d]; l++; 
                    }
                    xx -= dx[d]; yy -= dy[d]; l--;   // Then move one step back. 'l' = number of steps.

                    if (l > 0) {        // Did we move at all?
                        if (spath[xx][yy] == -1 ||
                            spath[x][y]+l < spath[xx][yy]) {    // Is the number of steps better than what we already has?
                                isnew[xx][yy] = true;
                                spath[xx][yy] = spath[x][y] + l;   // If so, update the number and mark the position as 'new'.
                                changed = true;
                        }
                    }
                }
            }
    }

    out.println(spath[sx][sy]);       // Read off the value at Daddy's position.
}