for (int i = 1; i <= a; ++i) {
if (i > 1)
System.out.println(); // more than 1 line, need delimiter (new line)
for (int j = 1; j <= i; ++j) {
if (j > 1)
System.out.print(" "); // more than 1 column, need delimiter (space)
System.out.print(j);
}
}