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 |
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1 | tourist | 3690 |
2 | jiangly | 3647 |
3 | Benq | 3581 |
4 | orzdevinwang | 3570 |
5 | Geothermal | 3569 |
5 | cnnfls_csy | 3569 |
7 | Radewoosh | 3509 |
8 | ecnerwala | 3486 |
9 | jqdai0815 | 3474 |
10 | gyh20 | 3447 |
# | User | Contrib. |
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1 | maomao90 | 174 |
2 | awoo | 165 |
3 | adamant | 161 |
4 | TheScrasse | 160 |
5 | nor | 158 |
6 | maroonrk | 156 |
7 | -is-this-fft- | 152 |
8 | orz | 146 |
9 | SecondThread | 145 |
9 | pajenegod | 145 |
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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