POJ 3160 Father Christmas flymouse（强连通分量+spfa最长路）

最近老是莫名其妙1A。

////  main.cpp//  Richard////  Created by 邵金杰 on 16/8/18.//  Copyright © 2016年 邵金杰. All rights reserved.//#include<iostream>#include<cstdio>#include<vector>#include<cstring>#include<algorithm>#include<queue>using namespace std;const int maxn=30000+100;int dfn[maxn],low[maxn],belong[maxn],w[maxn],instack[maxn],in[maxn],dist[maxn],tree[maxn];vector<vector<int> > G(maxn);vector<vector<int> > map(maxn);vector<int> s;int n,m;int color,idex;void tarjan(int u){    dfn[u]=low[u]=++idex;    s.push_back(u);    instack[u]=1;    for(int i=0;i<G[u].size();i++)    {        int v=G[u][i];        if(!dfn[v])        {            tarjan(v);            low[u]=min(low[u],low[v]);        }        else if(instack[v])        {            low[u]=min(low[u],dfn[v]);        }    }    if(dfn[u]==low[u])    {        int p;        color++;        int sum=0;        do{            p=s[s.size()-1];            instack[p]=0;            sum+=w[p];            belong[p]=color;            s.pop_back();        }while(u!=p);        tree[color]=sum;    }}void creat_graph(){    for(int i=0;i<n;i++)    {        for(int j=0;j<G[i].size();j++)        {            int v=G[i][j];            if(belong[i]!=belong[v])            {                in[belong[v]]++;                map[belong[i]].push_back(belong[v]);            }        }    }    for(int i=1;i<=color;i++)    {        if(in[i]==0) {map[color+1].push_back(i);}    }}int spfa(){    memset(dist,0,sizeof(dist));    queue<int> q;    q.push(color+1);    while(!q.empty())    {        int s=q.front();        q.pop();        for(int i=0;i<map[s].size();i++)        {            int e=map[s][i];            if(dist[e]<dist[s]+tree[e])            {                dist[e]=dist[s]+tree[e];                q.push(e);            }        }    }        sort(dist+1,dist+color+2);    return dist[color+1];}int main(){    while(scanf("%d%d",&n,&m)!=EOF)    {        color=0,idex=0;        for(int i=0;i<n;i++) G[i].clear(),map[i].clear();        map[n].clear();        s.clear();        memset(dfn,0,sizeof(dfn));        memset(low,0,sizeof(low));        memset(belong,0,sizeof(belong));        memset(w,0,sizeof(w));        memset(instack,0,sizeof(instack));        memset(in,0,sizeof(in));        memset(dist,0,sizeof(dist));        memset(tree,0,sizeof(tree));        for(int i=0;i<n;i++){            scanf("%d",&w[i]);            if(w[i]<0) w[i]=0;        }        int a,b;        for(int i=0;i<m;i++)        {            scanf("%d%d",&a,&b);            G[a].push_back(b);        }        for(int i=0;i<n;i++)        {            if(!dfn[i])            {                tarjan(i);            }        }        creat_graph();        printf("%d\n",spfa());    }    return 0;}