入门经典-习题7-1,109-uva208消防车-DFS，并查集，打印路径，利用set保存边，字典序，STL⭐⭐⭐⭐⭐复杂度：3

#include<cstdio>
#include<iostream>
#include<cstring>
#include<vector>
#include<map>
#include<set>
#include<sstream>
#include<algorithm>//find()
using namespace std;
const int maxn=20+5;
int N,pa[maxn];
set<int> G[maxn];
int find_pa(int x){
	return x==pa[x]?x:(pa[x]=find_pa(pa[x]));
}

ostream& operator<<(ostream& os,const vector<int>& s){
	bool first=true;
	for(int i=0;i<s.size();i++){
		if(first) first=false;
		else os<<" ";
		os<<s[i];
	}
	return os;
}

vector<int> path;
vector<string> paths;
int vis[maxn];
void dfs(int src,int dest){
	path.push_back(src);
	vis[src]=1;
	int v;
	if(src==dest){
		stringstream os; os<<path;
		paths.push_back(os.str());
	}
	else {
		for(set<int>::iterator it=G[src].begin();it!=G[src].end();it++){
			v=*it;
			if(vis[v])//
			continue;
			dfs(v,dest);
			//vis[v]=0; ① 
			//path.pop_back(); ② （删除v） 
		}
	}
	vis[src]=0;// ③  可删除③④语句换成①② 两个方法完全等价 
	path.pop_back();// ④ （删除src ） 
	
}
int main(){
	for(int kase=1,from,to;scanf("%d",&N)==1;kase++){
		for(int i=0;i<maxn;i++) G[i].clear(),pa[i]=i;//
		paths.clear(),path.clear();
		memset(vis,0,sizeof(vis));
		while(true){
			cin>>from>>to;
			if(from==0||to==0)
			break;
			G[from].insert(to),G[to].insert(from);
			int pf=find_pa(from),pt=find_pa(to);
			if(pf!=pt)
			pa[pt]=pf;
		}
		
		if(find_pa(1)==find_pa(N)) dfs(1,N);//先判断连通 连通再dfs 
		printf("CASE %d:\n",kase);
		for(int i=0;i<paths.size();i++){
			cout<<paths[i]<<endl;
		}
		printf("There are %lu routes from the firestation to streetcorner %d.\n",paths.size(),N);
	}
	return 0;
}