[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 100050using 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\n");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\n",ans);    return 0;}