1996: [USACO 2023 US Open Contest Bronze] Problem 1. FEB

Bessie and Elsie are plotting to overthrow Farmer John at last! They plan it out over $N$ ($1\le N\le 2\cdot {10}^5$) text messages. Their conversation can be represented by a string $S$ of length $N$ where $S_i$ is either $B$ or $E$, meaning the $i$th message was sent by Bessie or Elsie, respectively.

However, Farmer John hears of the plan and attempts to intercept their conversation. Thus, some letters of $S$ are $F$, meaning Farmer John obfuscated the message and the sender is unknown.

The excitement level of a non-obfuscated conversation is the number of times a cow double-sends - that is, the number of occurrences of substring $BB$ or $EE$ in $S$. You want to find the excitement level of the original message, but you don’t know which of Farmer John’s messages were actually Bessie’s / Elsie’s. Over all possibilities, output all possible excitement levels of $S$.

The next line contains $S$.

4
BEEF

2
1
2