Logu P1595 envelope problem, logu p1595 envelope

Logu P1595 envelope problem, logu p1595 envelope
Description

Someone wrote n letters and n envelopes, if all the letters were wrong. The number of different situations in which the wrong envelope is loaded for all messages.

Input/Output Format

Input Format:

 

Number of envelopes n (n <= 20)

 

Output Format:

 

An integer represents the number of cases.

 

Input and Output sample input sample #1: Copy

2

Output example #1: Copy

1

Input example #2: Copy

3

Output sample #2: Copy

2

 

Recursive Formula: $ f [n] = (n-1) * (f [n-1] + f [N-2]) $

# Include <iostream> # include <cstdio> using namespace std; int main () {int N; cin> N; int a1 = 0, a2 = 1, a3; for (int I = 3; I <= N; I ++) {a3 = (I-1) * (a1 + a2); a1 = a2, a2 = a3 ;} if (N = 1) cout <a1; else if (N = 2) cout <a2; else cout <a3; return 0 ;}