洛谷P3627 [APIO2009]抢掠计划——题解

题目传送门
题目大意：
看题面吧。

---

思考过程&具体做法：
先缩点，然后从市中心所在的新点开始做dp，最后对有酒吧的新点统计答案。

---

代码：

#include <bits/stdc++.h>
using namespace std;

const int maxn=5e5+1000;
struct stu
{
    int to,next;
}road[maxn],newroad[maxn]; int first[maxn],cnt=0,last[maxn],cnt1=0;
struct lily
{
    int x,y;
}len[maxn];
int n,m,top,colnum,s,p,ans;
int dfn[maxn],low[maxn],sta[maxn],book[maxn],mark[maxn],sum[maxn],col[maxn],pub[maxn],money[maxn],dp[maxn];
queue <int> q;

void addedge(int x,int y)
{
    road[++cnt].to=y;
    road[cnt].next=first[x];
    first[x]=cnt;
}

void tarjan(int now)
{
    dfn[now]=low[now]=++cnt;
    sta[++top]=now;
    book[now]=1;
    for(int i=first[now];i;i=road[i].next)
    {
        int to=road[i].to;
        if(!dfn[to]) { tarjan(to);low[now]=min(low[now],low[to]); }
        else if(book[to]) low[now]=min(low[now],dfn[to]);
    }
    if(low[now]==dfn[now])
    {
        colnum++;
        while(top>=1&&sta[top]!=now)
        {
            if(pub[sta[top]]) mark[colnum]=1;
            sum[colnum]+=money[sta[top]];
            book[sta[top]]=0;
            col[sta[top]]=colnum;
            top--;
        }
        if(pub[sta[top]]) mark[colnum]=1;
        sum[colnum]+=money[sta[top]];
        book[sta[top]]=0;
        col[sta[top]]=colnum;
        top--;
    }
}

bool cmp1(lily t1,lily t2)
{
    return t1.x==t2.x?t1.y<t2.y:t1.x<t2.x;
}

void add_newedge(int x,int y)
{
    newroad[++cnt1].to=y;
    newroad[cnt1].next=last[x];
    last[x]=cnt1;
}

int main()
{
//    freopen("45.in","r",stdin);
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        addedge(x,y);
        len[i].x=x,len[i].y=y;
    }
    for(int i=1;i<=n;i++) scanf("%d",&money[i]);
    scanf("%d%d",&s,&p);
    for(int i=1;i<=p;i++)
    {
        int x;
        scanf("%d",&x);
        pub[x]=1;
    }
    cnt=0;
//  cout<<1<<endl;
    for(int i=1;i<=n;i++)
        if(!dfn[i])
        {
            tarjan(i);
        }
//    cout<<1<<endl;
    for(int i=1;i<=m;i++)
    {
        len[i].x=col[len[i].x];
        len[i].y=col[len[i].y];
    }
    sort(len+1,len+1+m,cmp1);
    for(int i=1;i<=m;i++)
    {
        int x=len[i].x,y=len[i].y;
        if(x==y||(x==len[i-1].x&&y==len[i-1].y)) continue;
        add_newedge(x,y);
    }
    memset(book,0,sizeof(book));
    q.push(col[s]);
    dp[col[s]]=sum[col[s]];
    book[col[s]]=1;
    while(!q.empty())
    {
        int now=q.front();q.pop();book[now]=0;
        for(int i=last[now];i;i=newroad[i].next)
        {
            int to=newroad[i].to;
            dp[to]=max(dp[to],dp[now]+sum[to]);
            if(!book[to]) { book[to]=1; q.push(to); }
        }
    }
    for(int i=1;i<=colnum;i++)
        if(mark[i]) ans=max(ans,dp[i]);
    printf("%d\n",ans);
    return 0;
}