題目大意
輸入 $n(1\le n)$，輸出 $1\sim n$ 錯排的數量。一個排列中所有的元素都不在自己原來的位置就被稱為錯排。
解法
設 $D_n$ 表示 $1\sim n$ 錯排的數量。已知 $D_1=0,D_2=1$ 。
1. 找規律
暴力列出 $n$ 比較小的 case，可以簡單地發現一個規律：
$$D_n=n\times D_{n-1}+(-1)^n$$
jacky860226 changed 2 years agoView mode Like BookmarkAre you sure to leave this team?
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