2017 Multi-University Training Contest
来源:互联网 发布:手机电流测试软件 编辑:程序博客网 时间:2024/06/05 16:15
题意:给你m种字符,让你填充两个长度为n的字符串,要求两个字符串不能有相同的字符,问最多有多少种填法。
n,m<=2000
思路:解这题的关键是解决用恰好k个字符去填充长度为n的字符有多少种方案。比赛时知道容斥可以做,但没想出
来。。所以用了第二类斯特林去做,第二类斯特林数(点击打开链接):把p元素集合划分到k个不可区分的盒子里且
没有空盒子的划分个数。在这就是看作n个位置填充k个颜色,因为颜色可区分,所以要成k的阶乘。
容斥做法:
第二类斯特林代码:
#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>using namespace std;typedef long long ll;const int mod = 1e9+7;const int maxn = 2e3+5;ll s[maxn][maxn], c[maxn][maxn], fac[maxn];void init(){ memset(s, 0, sizeof(s)); s[1][1] = 1; for(int i = 2; i < maxn; i++) for(int j = 1; j <= i; j++) s[i][j] = (s[i-1][j-1]+(ll)j*s[i-1][j])%mod; fac[0] = fac[1] = 1; for(int i = 2; i < maxn; i++) fac[i] = fac[i-1]*i%mod; for(int i = 1; i < maxn; i++) for(int j = 0; j <= i; j++) { if(i == j || !j) c[i][j] = 1; else c[i][j] = (c[i-1][j]+c[i-1][j-1])%mod; }}ll qpow(ll p, int q){ ll ans = 1; while(q) { if(q%2) ans = ans*p%mod; p = p*p%mod; q /= 2; } return ans;}int main(void){ init(); int n, m, t; cin >> t; while(t--) { scanf("%d%d", &n, &m); ll ans = 0; int e = min(n, m-1); for(int i = 1; i <= e; i++) { ans = (ans + s[n][i]*fac[i]%mod*qpow(m-i, n)%mod*c[m][i]%mod)%mod; } printf("%lld\n", ans%mod); } return 0;}
容斥代码:
#include<bits/stdc++.h>using namespace std;const int maxn = 3e3+5;const int mod = 1e9+7;typedef long long ll;ll c[maxn][maxn], rec[maxn], fac[maxn];void init(){ fac[0] = fac[1] = 1; for(int i = 2; i < maxn; i++) fac[i] = fac[i-1]*i%mod; for(int i = 1; i < maxn; i++) for(int j = 0; j <= i; j++) if(!j || i==j) c[i][j] = 1; else c[i][j] = (c[i-1][j]+c[i-1][j-1])%mod;}ll qmod(ll x, int p){ ll ans = 1; while(p) { if(p%2) ans = ans*x%mod; x = x*x%mod; p /= 2; } return ans;}int main(void){ init(); int t, n, m; cin >> t; while(t--) { scanf("%d%d", &n, &m); for(int i = 1; i <= n; i++) { rec[i] = qmod(i, n); for(int j = 1; j < i; j++) rec[i] = (rec[i]-c[i][j]*rec[j]%mod+mod)%mod; } ll ans = 0; for(int i = 1; i <= min(n, m-1); i++) ans = (ans+c[m][i]*rec[i]%mod*qmod(m-i, n)%mod)%mod; printf("%lld\n", ans); } return 0;}
阅读全文
0 0
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- #2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- #2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- 2017 Multi-University Training Contest
- Bigdata Development Web_Study_04(Session和Cookie)
- Color the ball||HDU1556
- dubbo配置方式(下)
- 编译错误:Failed to save the updated manifest to the file ..........
- [opengl笔记]2017年8月17日
- 2017 Multi-University Training Contest
- C
- 配置NC65与安装UAP-STUDIO中遇到的问题总结
- HTML5入门—DAY1:HTML基础
- cs224n assignment 2 代码
- HDU 6143 Killer Names(容斥+组合)
- windows下搭建spark环境
- 物联网开发必知的8大安全关键技术
- 线程并发问题