6 A B BA BB AA AB
0 1 2 5 10 25 * For $k=1$: There are no good subsets. * For $k=2$: There is $1$ good subset: $\lbrace S_1,S_2\rbrace$. * For $k=3$: There are $2$ good subsets: $\lbrace S_1,S_2\rbrace$, $\lbrace S_1,S_2,S_3\rbrace$. * For $k=4$: There are $5$ good subsets: $\lbrace S_1,S_2\rbrace$, $\lbrace S_1,S_2,S_3\rbrace$, $\lbrace S_1,S_2,S_4\rbrace$, $\lbrace S_1,S_3,S_4\rbrace$, $\lbrace S_1,S_2,S_3,S_4\rbrace$.
10 A B AABA AABB AB AA AAA BB AAB BA
0 1 2 4 8 20 41 82 170 425
{
"problem": {
"name": "Prefix Covering",
"description": {
"content": "A non-empty string where every character is `A` or `B` is called an **AB string**. A set $X$ consisting of AB strings is called a **good set** when it satisfies the following: * Every AB string of ",
"description_type": "Markdown"
},
"platform": "AtCoder",
"limit": {
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"memory_limit": 262144
},
"difficulty": "None",
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"is_sync": true,
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"sign": "arc201_c"
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"statements": [
{
"statement_type": "Markdown",
"content": "A non-empty string where every character is `A` or `B` is called an **AB string**.\nA set $X$ consisting of AB strings is called a **good set** when it satisfies the following:\n\n* Every AB string of ...",
"is_translate": false,
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}