uestc 方老师的分身 III 拓扑排序

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 }