杭电-2641 Reward（拓扑排序）

Reward

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 7528    Accepted Submission(s): 2377

Problem Description

Dandelion's uncle is a boss of a factory. As the spring festival is coming , he wants to distribute rewards to his workers. Now he has a trouble about how to distribute the rewards.
The workers will compare their rewards ,and some one may have demands of the distributing of rewards ,just like a's reward should more than b's.Dandelion's unclue wants to fulfill all the demands, of course ,he wants to use the least money.Every work's reward will be at least 888 , because it's a lucky number.

 

Input

One line with two integers n and m ,stands for the number of works and the number of demands .(n<=10000,m<=20000)
then m lines ,each line contains two integers a and b ,stands for a's reward should be more than b's.

Output

For every case ,print the least money dandelion 's uncle needs to distribute .If it's impossible to fulfill all the works' demands ,print -1.

 

Sample Input

2 11 22 21 22 1

 

Sample Output

1777-1

 

Author

dandelion

 

Source

曾是惊鸿照影来

 

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#include<cstdio>  #include<cstring>  #include<queue>  using namespace std;  int n,indegree[10010];  int head[20010],num[10010];    struct node  {      int to,next;  }map[20010];    void tuopu()  {      int i,top,k=0,sum=0;      queue<int>q;      for(i=1;i<=n;++i)      {          if(indegree[i]==0)             q.push(i);      }      while(!q.empty())      {          top=q.front();          q.pop();          k++;//用k标记是否满足所有人需求，即不出现环           for(i=head[top];i!=-1;i=map[i].next)          {              indegree[map[i].to]--;              if(indegree[map[i].to]==0)              {                  q.push(map[i].to);                  num[map[i].to]=num[top]+1; //将下一层节点含有的值加一               }          }      }      for(i=1;i<=n;++i)         sum+=num[i];      if(k==n)//k等于n，则有向图中无环          printf("%d\n",sum);      else         printf("-1\n");   }    int main()  {      int m,i,a,b;      while(scanf("%d%d",&n,&m)!=EOF)      {          memset(indegree,0,sizeof(indegree));          memset(head,-1,sizeof(head));          for(i=1;i<=n;++i)             num[i]=888;          for(i=0;i<m;++i)          {              scanf("%d%d",&a,&b);//反向存表               map[i].to=a;              map[i].next=head[b];              head[b]=i;              indegree[a]++;          }          tuopu();      }      return 0;  }