poj 3160【tarjan縮點+拓撲排序+DP】

http://poj.org/problem?id=3160

方法：tarjan縮點+topsort+dp，注意這句話. To save vigor, flymouse decided to choose only one of those rooms as the place to start his journey and follow directed paths to visit one room after another and give out gifts en passant until he could reach
no more unvisited rooms.（就是說，他從一個點出發，一直走下去，假如縮點後有多個孤立點，他只能選擇其中一個）

code：

#include <vector>#include <list>#include <map>#include <set>#include <queue>#include <string.h>#include <deque>#include <stack>#include <bitset>#include <algorithm>#include <functional>#include <numeric>#include <utility>#include <sstream>#include <iostream>#include <iomanip>#include <cstdio>#include <cmath>#include <cstdlib>#include <limits.h>using namespace std;#define LL long long#define pi acos(-1)#define N  30010#define INF INT_MAX#define eps 1e-8//*********************************************//poj 3160 tarjan + top//*********************************************vector<int> v[N];vector<int> top[N];stack<int> st;int low[N],dfn[N],in[N],belong[N];int val[N],vv[N],vvm[N];bool inStack[N],vis[N];int time,num;int n,m;int min(int a,int b){    return a>b?b:a;}int max(int a,int b){    return a>b?a:b;}void tarjan(int u){    int i;    vis[u]=1;    st.push(u);    inStack[u]=1;    time++;    low[u]=time,dfn[u]=time;    for(i=0;i<v[u].size();i++)    {        int x=v[u][i];        if(!vis[x])        {            tarjan(x);            low[u]=min(low[u],low[x]);        }        else        if(inStack[x])            low[u]=min(low[u],dfn[x]);    }    if(low[u]==dfn[u])    {        num++;        while(1)        {            int x=st.top();            st.pop();            belong[x]=num;            vv[num]+=val[x];            inStack[x]=0;            if(x==u)break;        }    }}void work(){    int i,j,k;    for(i=0;i<n;i++)        for(j=0;j<v[i].size();j++)        {            int x=v[i][j];            if(belong[i]!=belong[x])            {                in[belong[x]]++;                top[belong[i]].push_back(belong[x]);            }        }    queue<int> q;    for(i=1;i<=num;i++)    if(in[i]==0)    {        q.push(i);        vvm[i]=vv[i];    }    while(!q.empty())    {        int x=q.front();        q.pop();        for(i=0;i<top[x].size();i++)        {            int y=top[x][i];            in[y]--;            vvm[y]=max(vvm[y],vvm[x]+vv[y]);            if(in[y]==0)            q.push(y);        }    }    int ans=0;    for(i=1;i<=num;i++)        ans=max(ans,vvm[i]);    printf("%d\n",ans);}int main(){freopen("a.txt","r",stdin);    while(scanf("%d%d",&n,&m)!=EOF)    {        int i,j,k;        for(i=0;i<=n;i++)        {            vis[i]=inStack[i]=low[i]=dfn[i]=vv[i]=vvm[i]=belong[i]=val[i]=in[i]=0;            v[i].clear();            top[i].clear();        }        while(!st.empty())st.pop();        for(i=0;i<n;i++)        {            scanf("%d",&val[i]);            if(val[i]<0)val[i]=0;        }        while(m--)        {            int a,b;            scanf("%d%d",&a,&b);            v[a].push_back(b);        }        time=0,num=0;        for(i=0;i<n;i++)        if(!vis[i])        tarjan(i);        work();    }    return 0;}