0
          12
         345
        6789
       01234
      567890
     1234567
    89012345
   678901234
  5678901234
 56789012345
678901234567
int line, i, j, k;

i = 0;
cout << "请输入行数：";
cin >> line;
for (j = 0; j < line; j++) {
    for (k = 0; k < ___________; k++) // L1
        cout << " ";
    for (k = 0; k < j + 1; k++) {
        cout << i;
        i += 1;
        if (i >= 10)
            i = 0;
    }
    cout << endl;
}