洛谷P3627 [APIO2009]抢掠计划

考试的时候一看就把大概的思路想出来了，结果tarjan缩点还没看，mmdd
思路：tarjian求强连通分量+缩点连边+SPFA最长路
code如下

#include<bits/stdc++.h>
#define re register int
using namespace std;
int n, m, t, cnt, st, ans, root, s, p, vis[500010], dfn[500010], low[500010], money[500010], wine[500010], belong[500010], d[500010], dis[500010];
vector<int>Edge[500010],edge[500010];
stack<int>stk;
int read()
{
    int ans = 0;
    char w = ' ', ch = getchar();
    while(ch < '0' || ch > '9')
    {
        w = ch;
        ch = getchar();
    }
    while(ch >= '0' && ch <= '9')
    {
        ans = (ans << 3) + (ans << 1);
        ans += ch - '0';
        ch = getchar();
    }
    return (w == '-' ? -ans : ans);
}
void tarjan(int x)
{
    dfn[x] = low[x] = ++t;
    stk.push(x);
    vis[x]=1;
    for(re j = 0; j < Edge[x].size(); j++)
    {
        int y = Edge[x][j];
        if(!dfn[y])
        {
            tarjan(y);
            low[x] = min(low[x], low[y]);
        }
        else if(vis[y])
        {
            low[x] = min(dfn[y], low[x]);
        }
    }
    if(dfn[x]==low[x])
    {
        cnt++;
        int z=0;
        do
        {
            z=stk.top();
            stk.pop();
            if(z==s) st=cnt;
            vis[z]=0;
            belong[z]=cnt;
            d[cnt]+=money[z];
        }while(z!=x);
    }
}
void SPFA(int x)
{
    queue<int>q;
    memset(vis,0,sizeof(vis));
    memset(dis,-1,sizeof(dis));
    q.push(x);
    vis[x]=1;
    dis[x]=d[x];
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        vis[u]=0;
        for(re j=0;j<edge[u].size();j++)
        {
            int v=edge[u][j];
            if(dis[v]<dis[u]+d[v])
            {
                dis[v]=dis[u]+d[v];
                if(!vis[v])
                {
                    vis[v]=1;
                    q.push(v);
                }
            }
        }
    }
}
int main()
{
	//freopen("atm.in","r",stdin);
	//freopen("atm.out","w",stdout);
    int a1, a2;
    n=read();m=read(); 
    for(re i = 1; i <= m; i++)
    {
        a1 = read();
        a2 = read();
        Edge[a1].push_back(a2);
    }
    for(re i=1;i<=n;i++)
    {
    	money[i]=read();
    }
    s=read();p=read();
    for(re i=1;i<=p;i++)
    {
    	wine[i]=read();
    }
    for(re i=1;i<=n;i++)
    {
        if(!dfn[i])
        {
            tarjan(i);
        }
    }
    for(re i=1;i<=n;i++)
    {
        for(re j=0;j<Edge[i].size();j++)
        {
            if(belong[i]!=belong[Edge[i][j]])
            {
                edge[belong[i]].push_back(belong[Edge[i][j]]);
            }
        }
    }
    SPFA(st);
    for(re i=1;i<=p;i++)
    {
        ans=max(ans,dis[belong[wine[i]]]);
    }
    cout<<ans;
    return 0;
}