HDOJ 1465 不容易系列之一

HDACM 1465

错排公式 f(n) = (n-1)(f(n-1)+f(n-2));
注意范围

import java.util.Scanner;public class Main{    public static void main(String[] args) {        Scanner sc = new Scanner(System.in);        while (sc.hasNext()) {            int n = sc.nextInt();            if (n==2) {                System.out.println(1);                continue;            }            long a = 0;            long b = 1;            long c = 0;            for (int i = 3; i <= n; i++) {                c = (i-1)*(a+b);                a = b;                b = c;            }            System.out.println(c);        }        sc.close();    }}