How to make a column based on previous values in dataframe

Use duplicated:

df['target'] = df.duplicated().astype(int)
print(df)

Output

   user_id                url  target
0      111         google.com       0
1      111        youtube.com       0
2      111        youtube.com       1
3      111         google.com       1
4      111  stackoverflow.com       0
5      111         google.com       1
6      222        twitter.com       0
7      222         google.com       0
8      222        twitter.com       1

df['target'] =df.groupby(['user_id','url']).cumcount().gt(0).astype(int)

    user_id            url      target
0      111         google.com       0
1      111        youtube.com       0
2      111        youtube.com       1
3      111         google.com       1
4      111  stackoverflow.com       0
5      111         google.com       1
6      222        twitter.com       0
7      222         google.com       0
8      222        twitter.com       1