sicily 4433 DAG?

题意：输入一个有向图，判断该图是否是有向无环图(Directed Acyclic Graph)。

解法：还是深搜

 1 #include<iostream>

 2 #include<memory.h>

 3 #include<stack>

 4 

 5 using namespace std;

 6 

 7 bool paths[101][101];

 8 int visited[101];

 9 bool isDAG;

10 int vertices,edges;

11 

12 void DFS(int current){

13     for(int j =1; isDAG == true && j <=vertices; j++){

14         if(paths[current][j] == true){

15             if(visited[j] == 0){

16                 visited[j] = 1;

17                 DFS(j);

18             }

19             else if(visited[j] == 1)

20                 isDAG = false;

21         }

22     }

23     //marked node as visted one stoping duplicated visiting when other visit trying to visit this pre-visit node

24     visited[current] = -1;

25 }

26 int main(){

27     int from,dest;

28     memset(paths,false,sizeof(paths));

29     memset(visited,0,sizeof(visited));

30     cin >> vertices >> edges;

31     for(int i=1;i<= edges;i++){

32         cin >> from >> dest;

33         paths[from][dest] = true;

34     }

35     //depth-first search checking every node

36     isDAG = true;

37     for(int i=1; isDAG == true && i <= vertices; i++){

38         if(visited[i] == 0){

39             visited[i] == 1;

40             DFS(i);

41         }

42     }

43     if(isDAG)

44         cout << 1 << endl;

45     else

46         cout << 0 << endl;

47     return 0;

48 }