把 $x$ 和 $2x+2$ 连一条边，则图是由一些链组成的，答案就是每条链长度除以 $2$ 上取整求和。
把 $n$ 加上 $2$，变成 $x$ 和 $2x$ 连边，最后只需答案减去 $1$（因为多了 $1$ 和 $2$）。
$x$ 和 $2x$ 连边时的答案就是 $n-\lfloor n/2\rfloor+\lfloor n/4\rfloor-\cdots$。这其实就是对每条链上进行容斥。
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Discussion #168 for Problem #4274. $2x + 2$
Type: Editorial
Status: Open
Posted by: jiangly
Posted at: 2025-12-12 23:47:46
Last updated: 2025-12-12 23:47:51
题解
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