[sicily online]1155. Can I Post the lette(圖的深度優先搜尋)

#include<iostream>#include<vector>#include<map>#include<algorithm>#include<fstream>#include<stack>#include<bitset>using namespace std;int main(){int n,m;while(cin>>n&&n!=0){cin>>m;map<int,vector<int> > gra;vector<bool> flag(n);for(int i=0;i<m;i++){int x,y;cin>>x>>y;gra[x].push_back(y);}//read edgebool result=false;flag[0]=true;stack<int> st;st.push(0);while(!st.empty())//深度優先遍曆{int top=st.top();st.pop();if(top==n-1){result=true;break;}for(int i=0;i<gra[top].size();i++){if(flag[gra[top][i]]==true)continue;flag[gra[top][i]]=true;st.push(gra[top][i]);}}if(result)cout<<"I can post the letter"<<endl;else cout<<"I can't post the letter"<<endl;}}