Poj 3160 [Tarjan contraction point + topological sorting + dp]

Http://poj.org/problem? Id = 3160

Method: Tarjan contraction point + topsort + dp. Pay attention to this sentence. 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 cocould reach
No more unvisited rooms)

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;}