How to fill new values in a data frame column based on some condition from other column

How to fill new values in a dataframe based on some condition from other column

For eg. I want to fill the rows which have the time as 11:30 in y column with value 1 in regressor column, while those dates having time 11:25 should be filled with value 2 in regressor column.

How to do this?

The type of input_df["ds"] column is pandas.core.series.Series

input_df

            ds             y    regressor
0   2019-10-04 11:30:00    a       0
1   2019-10-04 11:35:00    b       0
2   2019-10-04 11:40:00    c       0
3   2019-10-04 11:25:00    d       0
4   2019-10-04 11:50:00    e       0
.
.
.
n   2019-14-04 11:50:00    f       0

output_df

            ds             y    regressor
0   2019-10-04 11:30:00    a       1
1   2019-10-04 11:35:00    b       0
2   2019-10-04 11:40:00    c       0
3   2019-10-04 11:25:00    d       2
4   2019-10-04 11:50:00    e       0
.
.
.
n   2019-14-04 11:50:00    f       0

'''