POJ——T3160 Father Christmas flymouse

Time Limit: 1000MS   Memory Limit: 131072K
Total Submissions: 3496   Accepted: 1191

 

缩点，然后每个新点跑一边SPFA 

思路不难 ，注意细节~

  1 #include <algorithm>
  2 #include <cstring>
  3 #include <cstdio>
  4 #include <queue>
  5 
  6 using namespace std;
  7 
  8 const int M(150000+5);
  9 const int N(30000+15);
 10 int n,m,u,v,val[N],ans;
 11 
 12 int hed[N],had[N],sumedge;
 13 struct Edge
 14 {
 15     int v,next;
 16 }edge[M];
 17 void ins(int u,int v,int *head)
 18 {
 19     sumedge++;
 20     edge[sumedge].v=v;
 21     edge[sumedge].next=head[u];
 22     head[u]=sumedge;
 23 }
 24 
 25 int dfn[N],low[N],tim;
 26 int col[N],sumcol,cval[N];
 27 int Stack[N],instack[N],top;
 28 void DFS(int now)
 29 {
 30     dfn[now]=low[now]=++tim;
 31     Stack[++top]=now,instack[now]=1;
 32     for(int i=hed[now];i;i=edge[i].next)
 33     {
 34         int to=edge[i].v;
 35         if(!dfn[to]) DFS(to),low[now]=min(low[now],low[to]);
 36         else if(instack[to]) low[now]=min(low[now],dfn[to]);
 37     }
 38     if(low[now]==dfn[now])
 39     {
 40         col[now]=++sumcol;
 41         cval[sumcol]+=val[now];
 42         for(;Stack[top]!=now;top--)
 43         {
 44             col[Stack[top]]=sumcol;
 45             cval[sumcol]+=val[Stack[top]];
 46             instack[Stack[top]]=0;
 47         }
 48         instack[now]=0;top--;
 49     }
 50 }
 51 
 52 int rd[N];
 53 void Get_map()
 54 {
 55     for(u=1;u<=n;u++)
 56         for(int i=hed[u];i;i=edge[i].next)
 57         {
 58               v=edge[i].v;
 59               if(col[u]!=col[v])
 60               rd[col[v]]++,ins(col[u],col[v],had);
 61         }
 62 }
 63 
 64 queue<int>que;
 65 int inq[N],dis[N];
 66 int SPFA(int s)
 67 {
 68     int ret=dis[s]=cval[s];
 69     memset(inq,0,sizeof(inq));
 70     que.push(s);inq[s]=1;
 71     while(!que.empty())
 72     {
 73         u=que.front();que.pop(),inq[u]=0;
 74         for(int i=had[u];i;i=edge[i].next)
 75         {
 76             v=edge[i].v;
 77             if(dis[v]<dis[u]+cval[v])
 78             {
 79                 dis[v]=dis[u]+cval[v];
 80                 ret=max(ret,dis[v]);
 81                 if(!inq[v])
 82                     que.push(v),inq[v]=1;
 83             }
 84         }
 85     }
 86     return ret;
 87 }
 88 
 89 void init()
 90 {
 91     sumcol=sumedge=top=tim=ans=0;
 92     memset(rd,0,sizeof(rd));
 93     memset(hed,0,sizeof(hed));
 94     memset(had,0,sizeof(had));
 95     memset(dis,0,sizeof(dis));
 96     memset(col,0,sizeof(col));
 97     memset(dfn,0,sizeof(dfn));
 98     memset(low,0,sizeof(low));
 99     memset(val,0,sizeof(val));
100     memset(cval,0,sizeof(cval));
101     memset(Stack,0,sizeof(Stack));
102     memset(instack,0,sizeof(instack));
103 }
104 
105 int main()
106 {
107     while(~scanf("%d%d",&n,&m))
108     {
109         init();
110         for(int i=1;i<=n;i++)
111             scanf("%d",val+i),val[i]=max(0,val[i]);
112         for(int u,v;m--;)
113             scanf("%d%d",&u,&v),ins(u+1,v+1,hed);
114         for(int i=1;i<=n;i++) if(!dfn[i]) DFS(i);
115         Get_map();
116         for(int i=1;i<=sumcol;i++)
117             if(!rd[i]) ans=max(ans,SPFA(i));
118         printf("%d\n",ans);
119     }
120     return 0;
121 }

 

posted @ 2017-06-10 16:30  Aptal丶  阅读(183)  评论(0)  编辑  收藏  举报