80pts求助

#include<bits/stdc++.h>
using namespace std;
int read(){
	int x=0;
	char c=getchar();
	while(!isdigit(c)) c=getchar();
	while(isdigit(c)) x=x*10+(c-'0'),c=getchar();
	return x;
}
int n,m,x,y,a[500005],top;
vector<int> v[500005];
void dfs1(int x,int fa){
	a[++top]=x;
	for(int i=0;i<v[x].size();i++){
		if(v[x][i]==fa) continue;
		dfs1(v[x][i],x);
	}
}
bool flag[500005],f[500005];
int d[500005],lo[500005],s[500005],topp;
void dfs2(int x,int fa,int k){
	s[++topp]=x,flag[x]=1,d[x]=lo[x]=k;
	for(int i=0;i<v[x].size();i++){
		if(v[x][i]==fa) continue;
		if(flag[v[x][i]]){ lo[x]=min(lo[x],d[v[x][i]]);break; }
		dfs2(v[x][i],x,k+1),lo[x]=min(lo[x],lo[v[x][i]]);
	}
	if(lo[x]==k){
		bool flag1=0;
		while(s[topp]!=x)
			f[s[topp]]=1,topp--,flag1=1;
		if(flag1) f[x]=1;
		topp--;
	}
}
bool fff;
void dfs3(int x,int k){
	//cout<<x<<" "<<k<<"\n";
	a[++top]=x,flag[x]=1;
	for(int i=0;i<v[x].size();i++){
		if(flag[v[x][i]]) continue;
		if(f[v[x][i]]){
			int j=i+1;
			while(j<v[x].size()){
				if(!flag[v[x][j]]) break;
				j++;
			}
			if(j>=v[x].size()) j=k;
			else j=v[x][j];
			if(k==-2) dfs3(v[x][i],-1);
			else if(k==-1) dfs3(v[x][i],j);
			else if(i==v[x].size()-1&&v[x][i]>k&&!fff){ fff=1;continue; }
			else dfs3(v[x][i],j);
		}
		else dfs3(v[x][i],k);
	}
}
int main(){
	n=read(),m=read();
	for(int i=1;i<=m;i++){
		x=read(),y=read();
		v[x].push_back(y),v[y].push_back(x);
	}
	for(int i=1;i<=n;i++) sort(v[i].begin(),v[i].end());
	if(m==n-1){
		dfs1(1,0);
		for(int i=1;i<=n;i++) printf("%d ",a[i]);
	}
	if(m==n){
		dfs2(1,0,1);
		for(int i=1;i<=n;i++) flag[i]=0;
		//cout<<"---\n";
		v[0].push_back(1);
		dfs3(0,-2);
		for(int i=2;i<=n+1;i++) printf("%d ",a[i]);
	}
	return 0;
}