Codeforces 1263D Secret Passwords - Logic

Do not compare every string to every other string ($O(n^2)$). Connect every string to its letters!

Nodes $0 \ldots n-1$ are strings. Nodes $n \ldots n+25$ are letters (a-z).

For each string, union it with each of its letters. Strings sharing a letter become connected through that letter hub.

Finally, count distinct leaders among strings only. Time: $O(n \cdot L \cdot \alpha)$ where $L$ is average string length.

Space complexity is $O(n)$ for the data structures used.