卧薪尝胆,厚积薄发。
ZJOI2005 沼泽鳄鱼
Date: Sat Sep 15 13:15:33 CST 2018 In Category: NoCategory

Description:

一个无向图,会循环出现一些点不能在某个时刻到达,周期只可能是 $2,3,4$ ,问从 $s$ 到 $t$ 经过 $k$ 的路径条数。
$1\le n\le 50,1\le k\le2\times 10^9$

Solution:

$lcm(2,3,4)=12$ ,所以先构造 $12$ 个转移矩阵分别对应每个时间,可以先不考虑不能到达构造出一个矩阵,然后把不能到达的点在矩阵中删掉,然后把这 $12$ 个矩阵乘起来,设 $k=i\times 12+j$ ,对于 $i$ 用整个的矩阵算, $j$ 再单独算,之所以这样是因为矩阵乘法没有交换律所以不能把相同的合在一起。

Code:


#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<cstring>
using namespace std;
inline int read()
{
register int res = 0;
register char c = getchar();
while(!isdigit(c))c = getchar();
while(isdigit(c))
{
res = (res << 1) + (res << 3) + c - '0';
c = getchar();
}
return res;

}
int n,m,s,e,k;
int h;
#define MOD 10000
#define MAXN 51
struct matrix
{
int m[MAXN][MAXN];
matrix(){memset(m,0,sizeof(m));}
void init()
{
memset(m,0,sizeof(m));
for(int i = 1;i <= n;++i)m[i][i] = 1;
return;
}
friend matrix operator * (matrix a,matrix b)
{
matrix c;
for(int i = 1;i <= n;++i)
for(int j = 1;j <= n;++j)
for(int k = 1;k <= n;++k)
c.m[i][j] = (c.m[i][j] + a.m[i][k] * b.m[k][j] % MOD) % MOD;
return c;
}
friend matrix operator ^ (matrix a,int b)
{
matrix res;
if(b == 0)
{
res.init();
return res;
}
res = a;--b;
while(b > 0)
{
if(b & 1)res = res * a;
a = a * a;
b = b >> 1;
}
return res;
}
}f[13],tr,res;
bool ava[13][MAXN];
int main()
{
scanf("%d%d%d%d%d",&n,&m,&s,&e,&k);
++s;++e;
int a,b;
for(int i = 1;i <= m;++i)
{
a = read();b = read();
++a;++b;
tr.m[a][b] = tr.m[b][a] = 1;
}
for(int i = 1;i <= 12;++i)f[i] = tr;
scanf("%d",&h);
for(int i = 1;i <= h;++i)
{
a = read();
for(int j = 1;j <= a;++j)
{
b = read();++b;
for(int x = j - 1;x < 12;x += a)
for(int y = 1;y <= n;++y)
f[(x - 1 + 12) % 12 + 1].m[y][b] = 0;
}
}
f[0].init();
for(int i = 1;i <= 12;++i)f[0] = f[0] * f[i];
int bloc = k / 12,rem = k % 12;
res = f[0] ^ bloc;
for(int i = 1;i <= rem;++i)res = res * f[i];
cout << res.m[s][e] << endl;
return 0;
}
In tag: DP-矩阵加速
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