#include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;#define MAX 100struct Node{    int value;    struct Node* nextNode;};struct LGraph{    struct Node vertexs[MAX];        int ids[MAX];    int vexnum;    int edgenum;} lg;void create_lg(){    int u,v;     int i;    struct Node *pi;    for(i = 0; i < lg.edgenum; i++){        scanf("%d%d", &u, &v);             u --; v --;        pi = (struct Node*)malloc(sizeof(struct Node));        pi->value = v;        pi->nextNode = lg.vertexs[u].nextNode;        lg.vertexs[u].nextNode = pi;        lg.ids[v] ++;    }}void sort() {    int i;    int index = 0;    int count[MAX];    memset(count, 0, sizeof(count));    queue
         
           Q;       for(i = 0; i < lg.vexnum; i++){        if(0 == lg.ids[i]){            Q.push(i);             }         }    while(!Q.empty()){        int node;              struct Node * pi;        struct Node * tmp;        node = Q.front();        count[index++] = node;        Q.pop();        pi = lg.vertexs[node].nextNode;        while(pi){            int v = pi->value;                 lg.ids[v] --;            if(lg.ids[v] == 0) {                Q.push(v);            }            tmp = pi;            pi = pi->nextNode;            free(tmp);            lg.edgenum --;        }    }     if(index == lg.vexnum){        for(i = 0; i < index; i++){            if(i == 0){                printf("%d", count[i] + 1);                 }                 else{                printf(" %d", count[i] + 1);             }        }         printf("\n");    }    else{        printf("Network has a cycle!\n");         }      }void delete_lg(){    int i;    struct Node * pi;    for( i = 0; i < lg.vexnum; i++){        pi = lg.vertexs[i].nextNode;        while(pi) {            pi = pi->nextNode;                 free(pi);        }     }      }void init_lg(){    lg.vexnum = 0;    lg.edgenum = 0;        memset(lg.vertexs, 0, sizeof(lg.vertexs));    memset(lg.ids, 0, sizeof(lg.ids));    delete_lg();}int N, M;int main() {    int i;         while(1) {        scanf("%d%d", &N, &M);            if( 0 == N && 0 == M) {            break;             }        init_lg();        lg.vexnum = N;        lg.edgenum = M;              create_lg();        sort();    }    init_lg();    return 0;}
         
        
       
      
     

假设输入文件中有向图的格式为：首先是顶点个数 n 和边数 m；然后是每条边，每条边的数

据占一行，格式为 u v，表示从顶点 u 到顶点 v 的一条有向边，顶点序号从 1 开始计起。输入文件

最后一行为 0 0，表示输入数据结束。

样例输入：

6 8

1 2

1 4

2 6

3 2

3 6

5 1

5 2

5 6

6 8

1 3

1 2

2 5

3 4

4 2

4 6

5 4

5 6

0 0

样例输出： 

3 5 1 4 2 6

Network has a cycle!