spiral matrix i, ii

public List<Integer> (int[][] matrix) {
    List<Integer> ans = new ArrayList<Integer>();
    if (matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0)
        return ans;
    int rBegin = 0, cBegin = 0, rEnd = matrix.length - 1, cEnd = matrix[0].length - 1;
    while (rBegin <= rEnd && cBegin <= cEnd) {
        
        for (int i = cBegin; i <= cEnd; ++i) {
            ans.add(matrix[rBegin][i]);
        }
        rBegin += 1;
        // go down
        for (int i = rBegin; i <= rEnd; ++i) {
            ans.add(matrix[i][cEnd]);
        }
        cEnd -= 1;
        // go left
        if (rBegin > rEnd)
            break;
        for (int i = cEnd; i >= cBegin; --i)
            ans.add(matrix[rEnd][i]);
        rEnd -= 1;
        // go up
        if (cBegin > cEnd || rBegin > rEnd)
            break;
        for (int i = rEnd; i >= rBegin; --i)
            ans.add(matrix[i][cBegin]);
        cBegin += 1;
    }

    return ans;
}

public int[][] generateMatrix(int n) {
    int[][] board = new int[n][n];
    int rBegin = 0, rEnd = n - 1, cBegin = 0, cEnd = n - 1;
    int num = 1;
    while (rBegin <= rEnd && cBegin <= cEnd) {
        
        for (int i = cBegin; i <= cEnd; ++i) {
            board[rBegin][i] = num++;
        }
        rBegin += 1;
        // go down
        for (int i = rBegin; i <= rEnd; ++i) {
            board[i][cEnd] = num++;
        }
        cEnd -= 1;
        // go left
        if (rBegin > rEnd || cBegin > cEnd)
            break;
        for (int i = cEnd; i >= cBegin; --i) {
            board[rEnd][i] = num++;
        }
        rEnd -= 1;
        if (rBegin > rEnd || cBegin > cEnd)
            break;
        for (int i = rEnd; i >= rBegin; --i) {
            board[i][cBegin] = num++;
        }
        cBegin += 1;
    }
    return board;
}