P1613 跑路

预处理出所有一次能到的节点，然后floyd

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rint register int
ll n,m,mmap[55][55];
bool g[55][55][55];
void f()
{
    for(rint k=1;k<=50;k++)
    for(rint i=1;i<=n;i++)
    for(rint j=1;j<=n;j++)
    for(rint l=1;l<=n;l++)
    {
        if(g[i][j][k-1]&&g[j][l][k-1])
        {
            g[i][l][k]=true;
            mmap[i][l]=1;
        }
    }
}
void floyd()
{
    for(rint k=1;k<=n;k++)
    for(rint i=1;i<=n;i++)
    for(rint j=1;j<=n;j++)
    mmap[i][j]=min(mmap[i][j],mmap[i][k]+mmap[k][j]);
}
int main() {
    scanf("%lld%lld",&n,&m);
    ll u,v;
    memset(mmap,0x3f,sizeof(mmap));
    for(rint i=1;i<=m;i++)
    {
        scanf("%lld%lld",&u,&v);
        g[u][v][0]=true;
        mmap[u][v]=1;
    }
    f();
    floyd();
    printf("%lld\n",mmap[1][n]);
    return 0;
}