I have seen many time people starting dfs with starting node -1 but I don't understand why do they do this.Can you please tell me why do they do so like in this example.
# | User | Rating |
---|---|---|
1 | tourist | 4009 |
2 | jiangly | 3823 |
3 | Benq | 3738 |
4 | Radewoosh | 3633 |
5 | jqdai0815 | 3620 |
6 | orzdevinwang | 3529 |
7 | ecnerwala | 3446 |
8 | Um_nik | 3396 |
9 | ksun48 | 3390 |
10 | gamegame | 3386 |
# | User | Contrib. |
---|---|---|
1 | cry | 164 |
1 | maomao90 | 164 |
3 | Um_nik | 163 |
4 | atcoder_official | 160 |
5 | -is-this-fft- | 158 |
5 | adamant | 158 |
7 | awoo | 157 |
8 | TheScrasse | 154 |
8 | nor | 154 |
10 | djm03178 | 153 |
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It's not starting point, it's a parent of verticle in DFS's spannig tree. There is no parent of root of the spanning tree, so it's equal to -1