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  • CSUOJ 1525 Algebraic Teamwork

    Problem A

    Algebraic Teamwork

    The great pioneers of group theory and linear algebra want to cooperate and join their theories. In group theory, permutations – also known as bijective functions – play an important role. For a finite set A, a function σ : A A is called a permutation of A if and only if there is some function ρ : A A with σ(ρ(a)) = a and ρ(σ(a)) = a   for all a A.

    The other half of the new team – the experts on linear algebra – deal a lot with idempotent functions. They appear as projections when computing shadows in 3D games or as closure operators like the transitive closure, just to name a few examples. A function p : A A is called idempotent if and only if p(p(a)) = p(a)      for all a A.

    To continue with their joined research, they need your help. The team is interested in non-idempotent permutations of a given finite set A. As a first step, they discovered that the result only depends on the set’s size. For a concrete size 1 ≤ n ≤ 105, they want you to compute the number of permutations on a set of cardinality n that are not idempotent.

    Input

    The input starts with the number t ≤ 100 of test cases. Then t lines follow, each containing the set’s size 1 ≤ n ≤ 105.

    Output

    Output one line for every test case containing the number modulo 1000000007 = (109 + 7) of non-idempotent permutations on a set of cardinality n.

    Sample Input

    Sample Output

    3

    1

    2

    2171

    0

    1

    6425

    解题:n!-1

     1 #include <bits/stdc++.h>
     2 #define LL long long
     3 using namespace std;
     4 const int maxn = 100010;
     5 const int md = 1e9+7;
     6 LL d[maxn];
     7 int main(){
     8     d[0] = 1;
     9     for(int i = 1; i < maxn; ++i)
    10         d[i] = (i%md*d[i-1])%md;
    11     int x,ks;
    12     scanf("%d",&ks);
    13     while(ks--){
    14         scanf("%d",&x);
    15         printf("%lld
    ",(d[x]+md-1)%md);
    16     }
    17     return 0;
    18 }
    View Code
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  • 原文地址:https://www.cnblogs.com/crackpotisback/p/4344895.html
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