Finally, justice has been served to Bob!! 😭
In 2272F — Tree Reduction Game, Alice still gets the first move, but Bob finally gets some compensation: he can choose the initial root of the tree!
With the right choice, Bob can guarantee his victory even when playing second. No more suffering from always going second — Bob is finally getting his chance to shine!
Come on, Bob, you got this! 🗿
Upd: Bob really cooked this game. =DD
After a lot of research, the result surprised me
chart:n is the number of nodes in the tree
| n | samples | bob wins | alice wins | bob win rate |
| 2 | 1000 | 0 | 1000 | 0% |
| 3 | 1000 | 1000 | 0 | 100% |
| 4 | 1000 | 0 | 1000 | 0% |
| 5 | 1000 | 1000 | 0 | 100% |
| 6 | 1000 | 282 | 718 | 28.2% |
| 7 | 1000 | 1000 | 0 | 100% |
| 8 | 1000 | 463 | 537 | 46.3% |
| 9 | 1000 | 1000 | 0 | 100% |
| 10 | 1000 | 629 | 371 | 62.9% |
| 11 | 1000 | 1000 | 0 | 100% |
| 12 | 1000 | 735 | 265 | 73.5% |
| 13 | 1000 | 1000 | 0 | 100% |
| 14 | 1000 | 805 | 195 | 80.5% |
| 15 | 1000 | 1000 | 0 | 100% |
| 16 | 1000 | 875 | 125 | 87.5% |
| 17 | 1000 | 1000 | 0 | 100% |
| 18 | 1000 | 905 | 95 | 90.5% |
| 19 | 1000 | 1000 | 0 | 100% |
| 20 | 1000 | 934 | 66 | 93.4% |
| 21 | 1000 | 1000 | 0 | 100% |
| 22 | 1000 | 955 | 45 | 95.5% |
| 23 | 1000 | 1000 | 0 | 100% |
| 24 | 1000 | 967 | 33 | 96.7% |
| 25 | 1000 | 1000 | 0 | 100% |
| 26 | 1000 | 970 | 30 | 97% |
| 27 | 1000 | 1000 | 0 | 100% |
| 28 | 1000 | 979 | 21 | 97.9% |
| 29 | 1000 | 1000 | 0 | 100% |
| 30 | 1000 | 989 | 11 | 98.9% |
| .... | .... | .... | .... | .... |
| 90 | 1000 | 1000 | 0 | 100% |
| 91 | 1000 | 1000 | 0 | 100% |
| 92 | 1000 | 1000 | 0 | 100% |
| 93 | 1000 | 1000 | 0 | 100% |
| 94 | 1000 | 1000 | 0 | 100% |
| 95 | 1000 | 1000 | 0 | 100% |
| 96 | 1000 | 1000 | 0 | 100% |
| 97 | 1000 | 1000 | 0 | 100% |
| 98 | 1000 | 1000 | 0 | 100% |
| 99 | 1000 | 1000 | 0 | 100% |
| 100 | 1000 | 1000 | 0 | 100% |
It is easy to see that when n is odd, Bob always wins. If n is even, Bob's win rate increases gradually until it reaches 100%, regardless of the number of nodes (I tested n up to $$$10^5$$$).
proof:If anyone has found any proofs for this "interesting thing", feel free to share them in the comment, I will add them here. :)