没什么好说的。。
1 #include<iostream> 2 #include<cstdio> 3 #include<cstdlib> 4 #include<cstring> 5 #include<string> 6 #include<queue> 7 #include<algorithm> 8 #include<map> 9 #include<iomanip> 10 #include<climits> 11 #include<string.h> 12 #include<cmath> 13 #include<stdlib.h> 14 #include<vector> 15 #define INF 1e7 16 #define MAXN 100010 17 #define maxn 1000010 18 #define Mod 1000007 19 #define N 1010 20 using namespace std; 21 typedef long long LL; 22 23 int n, m; 24 int son[10001]; 25 int ans[10001]; 26 27 void init() 28 { 29 memset(son,0,sizeof(son)); 30 memset(ans,0,sizeof(ans)); 31 } 32 33 void process() 34 { 35 vector<int> G[10010]; 36 int x, y; 37 init(); 38 for (int i = 0; i < m; ++i) { 39 cin >> x >> y; 40 G[y].push_back(x); 41 son[x]++; 42 } 43 queue<int> q; 44 for (int i = 1; i <= n; ++ i) 45 if (son[i] == 0){ 46 q.push(i); 47 ans[i] = 888; 48 } 49 int res = n; 50 while (!q.empty()) { 51 int t = q.front(); 52 q.pop(); 53 res--; 54 for (int i = 0; i < G[t].size(); ++i) { 55 int v = G[t][i]; 56 if (--son[v] == 0) { 57 ans[v] = ans[t] + 1; 58 q.push(v); 59 } 60 } 61 } 62 if (res > 0) puts("-1"); 63 else { 64 int sum = 0; 65 for (int i = 1; i <= n; ++i) 66 sum += ans[i]; 67 cout << sum << endl; 68 } 69 } 70 71 int main() 72 { 73 while (cin >> n >> m) 74 process(); 75 return 0; 76 }