[Poi2012]Festival 差分约束+tarjan

差分约束建图，发现要在每个联通块里求最长路，600，直接O(n3) floyed

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#define N 650
#define M 100050
using namespace std;
int g[N][N],n,m1,m2,f[N],ans;
int e=1,head[N];
struct edge{
    int u,v,w,next;
}ed[2*M];
void add(int u,int v,int w){
    ed[e].u=u;ed[e].v=v;ed[e].w=w;
    ed[e].next=head[u];head[u]=e++;
    g[u][v]=min(g[u][v],w);
}
int dfn[N],low[N],top,q[N],tot,id[N];
bool bo[N];
void tarjan(int x){
    dfn[x]=low[x]=++top;
    q[top]=x;bo[x]=1;
    for(int i=head[x];i;i=ed[i].next){
        int v=ed[i].v;
        if(!dfn[v]){
            tarjan(v);
            low[x]=min(low[x],low[v]);
        }
        else if(bo[v])
            low[x]=min(low[x],dfn[v]);
    }
    if(low[x]==dfn[x]){
        int y;tot++;
        do{
            y=q[top--];
            bo[y]=0;
            id[y]=tot;
        }while(y!=x);
    }
}
int main(){
    memset(g,0x3f,sizeof g);
    scanf("%d%d%d",&n,&m1,&m2);
    for(int i=1;i<=n;i++)g[i][i]=0;
    int u,v;
    for(int i=1;i<=m1;i++){
        scanf("%d%d",&u,&v);
        add(u,v,1);add(v,u,-1);
    }
    for(int i=1;i<=m2;i++){
        scanf("%d%d",&u,&v);
        add(v,u,0);
    }
    for(int i=1;i<=n;i++)
        if(!dfn[i])
            tarjan(i);
    for(int k=1;k<=n;k++)
        for(int i=1;i<=n;i++)if(id[i]==id[k])
            for(int j=1;j<=n;j++)if(id[j]==id[i])
                g[i][j]=min(g[i][j],g[i][k]+g[k][j]);
    for(int i=1;i<=n;i++)
        if(g[i][i]<0){printf("NIE
");return 0;}
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
            if(id[i]==id[j])
                f[id[i]]=max(f[id[i]],g[i][j]+1);
    for(int i=1;i<=tot;i++) ans+=f[i];
    printf("%d
",ans);
    return 0;
}