HDU 2647

思路：拓扑排序

#include<stdio.h>
#include<string.h>
typedef struct
{
int to;
int next;
}EdgeNode;
EdgeNode Edge[20005];
int head[10005],node[10005];
int cnt,indegree[10005],vis[10005];
void init()
{
cnt = 0;
memset(vis,0,sizeof(vis));
memset(head,-1,sizeof(head));
memset(indegree,0,sizeof(indegree));
}

void add_edge(int n,int m)
{
Edge[cnt].to = n;
Edge[cnt].next = head[m];
head[m] = cnt++;
}

int main()
{
int n,m,a,b,i,j,k,t,p,sum;
while(~scanf("%d%d",&n,&m))
{
init();
sum = p = 0;
while(m--)
{
scanf("%d%d",&a,&b);
indegree[a]++;
add_edge(a,b);
}
for(i = 0;i < n;i ++)
{
t = 0;
for(j = 1;j <= n;j ++)
{
if(indegree[j] == 0 && vis[j] == 0)
node[t++] = j;
}
sum += (888+p)*t;
p++;
for(j = 0;j < t;j ++)
{
vis[node[j]] = 1;
for(k = head[node[j]];k != -1;k = Edge[k].next)
{
if(!vis[Edge[k].to])
indegree[Edge[k].to]--;
}
}
}
for(i = 1;i <= n;i ++)
{
if(indegree[i])
{
sum = -1;
break ;
}
}
printf("%d\n",sum);
}
return 0;
}