poj 3160 Father Christmas flymouse（Tarjan+SPFA）

2 2
14
21
0 1
1 0

35

#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <string.h>
#include <string>
#include <vector>
#include <queue>

#define MEM(a,x) memset(a,x,sizeof a)
#define eps 1e-8
#define MOD 10009
#define INF 0x3f3f3f3f
#define ll __int64
#define bug cout<<"here"<<endl
#define fread freopen("ceshi.txt","r",stdin)
#define fwrite freopen("out.txt","w",stdout)

using namespace std;

void read(int &x)
{
    char ch;
    x=0;
    while(ch=getchar(),ch!=' '&&ch!='\n')
    {
        x=x*10+ch-'0';
    }
}

const int MAXN=30010;
const int MAXM=150010;
struct Edge
{
    int to,next;
}edge[MAXM];
int head[MAXN],tot;
int low[MAXN],dfn[MAXN],sta[MAXN],belong[MAXN];
int Index,top;
int scc;
bool instack[MAXN];
int num[MAXN];
int n,m;
int a[MAXN];
int b[MAXN],c[MAXN];//用来存储点
int in[MAXN],out[MAXN];
vector<int> vec[MAXN];

void addedge(int u,int v)
{
    edge[tot].to=v; edge[tot].next=head[u]; head[u]=tot++;
}

void Tarjan(int u)
{
    int v;
    low[u]=dfn[u]=++Index;
    sta[top++]=u;
    instack[u]=1;
    for(int i=head[u];i!=-1;i=edge[i].next)
    {
        v=edge[i].to;
        if(!dfn[v])
        {
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(instack[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        scc++;
        do{
            v=sta[--top];
            instack[v]=0;
            belong[v]=scc;
            if(a[v]>0)
                num[scc]+=a[v];
        }while(u!=v);
    }
}

void solve()
{
    for(int i=1;i<=n;i++)
        if(!dfn[i])
            Tarjan(i);
}//Tarjan 部分

void init()
{
    MEM(head,-1);
    tot=0;
    MEM(dfn,0);
    MEM(num,0);
    MEM(instack,0);
    Index=scc=top=0;
    MEM(out,0);
    MEM(in,0);
}

struct EDGE
{
    int v,cost;
    EDGE(int _v,int _cost):v(_v),cost(_cost){}
};
vector<EDGE> E[MAXN];
void addEDGE(int u,int v,int w)
{
    E[u].push_back(EDGE(v,w));
}

bool vis[MAXN];
int dis[MAXN];
int SPFA(int start,int N)
{
    MEM(vis,0);
    for(int i=1;i<=N;i++) dis[i]=0;
    vis[start]=1;
    dis[start]=0;
    queue<int> que;
    while(!que.empty())  que.pop();
    que.push(start);
    while(!que.empty())
    {
        int u=que.front(); que.pop();
        vis[u]=0;
        for(int i=0;i<E[u].size();i++)
        {
            int v=E[u][i].v;
            if(dis[v]<dis[u]+E[u][i].cost)
            {
                dis[v]=dis[u]+E[u][i].cost;
                if(!vis[v])
                {
                    vis[v]=1;
                    que.push(v);
                }
            }
        }
    }
    int ans=0;
    for(int i=1;i<=N;i++)
    {
        if(out[i]==0)
            ans=max(ans,dis[i]);
    }
    return ans;

}

int main()
{
//    fread;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        init();
        for(int i=1;i<=n;i++)
            scanf("%d",&a[i]);
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d",&b[i],&c[i]);
            b[i]++; c[i]++;
            addedge(b[i],c[i]);
        }
        solve();
        for(int i=0;i<MAXN;i++)  E[i].clear();
        for(int i=1;i<=m;i++)
        {
            int u=belong[b[i]];
            int v=belong[c[i]];
            if(u!=v)
            {
                in[v]++;
                out[u]++;
                addEDGE(u,v,num[v]);
            }
        }
        for(int i=1;i<=scc;i++)
        {
            if(in[i]==0)
                addEDGE(0,i,num[i]);
        }
        int ans=SPFA(0,scc);
        printf("%d\n",ans);
    }
    return 0;
}