HDU2647+拓扑排序

先判断是否存在环。。然后dfs出每个人比几个人要求高。。

 1 ///*

 2 //拓扑

 3 //*/

 4 #include<stdio.h>

 5 #include<string.h>

 6 const int maxn =  10105;

 7 int ind[ maxn ],add[ maxn ],vis[ maxn ];

 8 struct node{

 9     int u,next;

10 }edge[ maxn<<2 ];

11 int cnt,head[ maxn ];

12 void init(){

13     cnt = 0;

14     memset( add,0,sizeof( add ) );

15     memset( head,-1,sizeof( head ) );

16     memset( vis,0,sizeof( vis ) );

17     memset( ind,0,sizeof( ind ) );

18 }

19 void addedge( int a,int b ){

20     edge[ cnt ].u = b;

21     edge[ cnt ].next = head[ a ];

22     head[ a ] = cnt++;

23 }

24 

25 int dfs( int cur ){

26     if( vis[ cur ]!=0 ) return add[ cur ];

27     //printf("cur=%d\n",cur);

28     vis[ cur ] = 1;

29     for( int i=head[ cur ];i!=-1;i=edge[ i ].next ){

30         //printf("nxt=%d\n",edge[i].u);

31         int dis = dfs( edge[ i ].u );

32         if( add[ cur ]<dis+1 ) add[ cur ] = dis+1;

33     }

34     return add[ cur ];

35 }

36 

37 int tuopu( int n ){

38     int cnt = 0;

39     for( int i=1;i<=n;i++ ){

40         int s = -1;

41         for( int j=1;j<=n;j++ ){

42             if( ind[ j ]<-1){

43                 return -1;

44             }

45             if( ind[ j ]==0 ){

46                 ind[ j ] = -1;

47                 s = j;

48                 cnt++;

49                 break;

50             }

51         }

52         //printf("s=%d\n",s);

53         if( s==-1 ) break;

54         for( int j=head[ s ];j!=-1;j=edge[ j ].next ){

55             ind[ edge[j].u ]--;

56             if( ind[ edge[j].u ]<-1 ) return -1;

57         }

58     }

59     if( cnt==n ) return 1;

60     else return -1;

61 }

62 

63 int main(){

64     int n,m;

65     while( scanf("%d%d",&n,&m)==2 ){

66         init();

67         int a,b;

68         while( m-- ){

69             scanf("%d%d",&a,&b);

70             ind[ b ]++;

71             addedge( a,b );

72         }

73 

74         int flag = tuopu( n );

75         if( flag==-1 ){

76             printf("-1\n");

77             continue;

78         }

79         //printf("flag=%d\n",flag);

80         for( int i=1;i<=n;i++ ){

81             if( vis[ i ]==0 ){

82                 dfs( i );

83             }

84         }

85         int sum = n*888;

86         //printf("sum=%d\n",sum);

87         for( int i=1;i<=n;i++ ){

88             sum+=add[i];

89             //printf("add[%d]=%d\n",i,add[i]);

90         }

91         printf("%d\n",sum);

92     }

93     return 0;

94 }

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