{"problem":{"name":"[USACO23OPEN] FEB B","description":{"content":"Bessie and Elsie are plotting to overthrow Farmer John at last! They plan it out over $N$ text messages. Their conversation can be represented by a string $S$ of length $N$ where $S_i$ is either `B` o","description_type":"Markdown"},"platform":"Luogu","limit":{"time_limit":2000,"memory_limit":262144},"difficulty":{"LuoguStyle":"P4"},"is_remote":true,"is_sync":true,"sync_url":null,"sign":"LGP9183"},"statements":[{"statement_type":"Markdown","content":"Bessie and Elsie are plotting to overthrow Farmer John at last! They plan it out\nover $N$ text messages. Their conversation can be\nrepresented by a string $S$ of length $N$ where $S_i$ is either `B` or `E`,\nmeaning the $i$ th message was sent by Bessie or Elsie, respectively. \n\nHowever, Farmer John hears of the plan and attempts to intercept their\nconversation. Thus, some letters of $S$ are `F`, meaning Farmer John obfuscated\nthe message and the sender is unknown.\n\nThe  **excitement level** of a non-obfuscated conversation is the number of\ntimes a cow double-sends - that is, the number of occurrences of substring `BB`\nor `EE` in $S$. You want to find the excitement level of the original message,\nbut you don’t know which of Farmer John’s messages were actually Bessie’s\n/ Elsie’s. Over all possibilities, output all possible excitement levels of\n$S$.\n\n## Input\n\nThe first line will consist of one integer $N$.\n\nThe next line contains $S$.\n\n## Output\n\nFirst output $K$, the number of distinct excitement levels possible. On the next\n$K$ lines, output the excitement levels, in increasing order.\n\n[samples]\n\n## Note\n\n$1\\le N\\le 2\\cdot 10^5$.\n\n- Inputs 4-8: $N\\le 10$.\n- Inputs 9-20: No additional constraints.","is_translate":false,"language":"English"}],"meta":{"iden":"LGP9183","tags":["数学","贪心","USACO","2023","分类讨论"],"sample_group":[["4\nBEEF\n","2\n1\n2\n"],["9\nFEBFEBFEB\n","2\n2\n3"],["10\nBFFFFFEBFE","3\n2\n4\n6"]],"created_at":"2026-03-03 11:09:25"}}