hdoj3664Permutation Counting【递推】
2015-11-27 21:04
309 查看
Permutation CountingTime Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 1519 Accepted Submission(s): 769 Problem Description Given a permutation a1, a2, … aN of {1, 2, …, N}, we define its E-value as the amount of elements where ai > i. For example, the E-value of permutation {1, 3, 2, 4} is 1, while the E-value of {4, 3, 2, 1} is 2. You are requested to find how many permutations of {1, 2, …, N} whose E-value is exactly k. Input There are several test cases, and one line for each case, which contains two integers, N and k. (1 <= N <= 1000, 0 <= k <= N). Output Output one line for each case. For the answer may be quite huge, you need to output the answer module 1,000,000,007. Sample Input 3 0 3 1 Sample Output 1 4 HintThere is only one permutation with E-value 0: {1,2,3}, and there are four permutations with E-value 1: {1,3,2}, {2,1,3}, {3,1,2}, {3,2,1} Source 2010 Asia Regional Harbin |
#include<cstdio> #include<cstdlib> #include<cstring> #include<algorithm> #include<cmath> #define MOD 1000000007 using namespace std; long long f[1010][1010]; void dabiao(){ f[1][1]=1; f[2][1]=1;f[2][2]=1; f[3][1]=1;f[3][2]=4;f[3][3]=1; for(int i=4;i<1010;++i){ f[i][1]=1; for(int j=2;j<=i;++j){ f[i][j]=(f[i-1][j-1]*(i-j+1)%MOD+(f[i-1][j]*j)%MOD)%MOD; } } } int main() { dabiao(); int n,k; while(scanf("%d%d",&n,&k)!=EOF){ printf("%lld\n",f [k+1]); } return 0; }
相关文章推荐
- hiho 14 并查集
- 数据库
- split 的 使用方法
- 2015.11.27初识java一集简单的java小程序
- CSS基础
- Web App开发入门
- nyoj 诡异的电梯【Ⅰ】 1070 (DP) 好题
- Linux压缩解压缩文章总结
- My way on Linux - 知识梳理计划
- 拉丁矩阵问题
- hdu 3466 Proud Merchants
- C语言端口扫描
- codeforces 412A Poster
- CodeForces 546C Soldier and Cards (队列)
- ViewPager
- objective - C 下字符串的处理方法
- Oracle例外处理
- PPT动画的若干问题
- 一些有用的HTML5 pattern属性
- TIMESTAMP类型插入到VARCHAR2后转成DATE类型和指定格式字符串