sicily 1155 Can I Post the letter

题意：判断有向图两点之间是否可通达！

解法：深搜或广搜(注意避免旧路重行)

　　

　　　DFS:

 #include<iostream>
 #include<vector>
 #include<string.h>
 using namespace std;

 struct Road{
     int From;
     int Dest;
     bool Vist;
     Road(int f,int d,bool v){
         From = f;
         Dest = d;
         Vist = v;
     }
 };
 vector<Road> roads[];
 bool reach=false;
 int N,M;

 void dfs(int n){
     if(n == N-){
         reach = true;
         return;
     }
     for(int i=;i<roads[n].size();i++){
         if(roads[n][i].Vist && roads[n][i].Dest !=){
             int gonext =roads[n][i].Dest;
             //use to avoid repeat search
             roads[n][i].Vist = false;
             dfs(gonext);
         }
     }
 }
 int main(){
     while(cin>>N && N>){
         cin>>M;
         reach = false;
         memset(roads,,sizeof(roads));
         int from,dest;
         bool exist = true;
         for(int i=;i<M;i++){
             cin >> from>>dest;
             Road r = Road(from,dest,exist);
             roads[from].push_back(r);
         }
         //deep search
         dfs();
         if(reach){
             cout<<"I can post the letter"<<endl;
         }
         else{
             cout<<"I can't post the letter"<<endl;
         }
     }
     return ;
 }

BFS:

 #include<iostream>
 #include<string.h>
 #include<queue>
 using namespace std;

 int N,M;
 int roads[][];
 bool visited[];

 int main(){
     while(cin>>N && N>){
         cin>>M;
         memset(roads,,sizeof(roads));
         memset(visited,false,sizeof(visited));
         int from=,dest=;
         for(int i=;i<M;i++){
             cin >> from>>dest;
             roads[from][dest] = ;
         }
         //breadth-first search
         queue<int> que;
         que.push();
         int i;
         while(!que.empty() && visited[N-] !=true){
             i = que.front();
             for(int j=;j<N;j++){
                 if(roads[i][j] ==  && visited[j] == false)
                 {
                     visited[j] = true;
                     que.push(j);
                 }
             }
             que.pop();
         }
         if(visited[N-] == true){
             cout<<"I can post the letter"<<endl;
         }
         else{
             cout<<"I can't post the letter"<<endl;
         }
     }
     return ;
 }