#10105. 「一本通 3.7 例 1」欧拉回路

求欧拉回路( dfs )

#include <bits/stdc++.h>
using namespace std ;
 const int N=1e6+3,M=2e6+3;
 
 
 
 inline int read(){
    int res = 0, flag = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            flag = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
    {
        res = res * 10 + ch - '0';
        ch = getchar();
    }
    return res * flag;
}
 int n,m;
 // op==1 有向图 op==2 无向图
 
 vector<int> ans;
 int deg[N],in[N],out[N];
 
 int nxt[M],go[M],hd[N],all;
 int op;
 int vis[N];
 void add_(int x,int y){
	nxt[++all]=hd[x]; hd[x]=all;
	go[all]=y;
 }
 
 void dfs(int x){
 	for(int &i=hd[x];i;i=nxt[i]){
 		int y=go[i];
 		int k=i;
 		
 		if(op==1){
 			int e=(i+1)/2;
 			if(vis[e]==0){
 				vis[e]=1;
 				dfs(y);
 				
 				if(k&1) ans.push_back(e);
 				else ans.push_back(-e);
 			}
 		}
 		else{
 			if(vis[k]==0){
 				vis[k]=1;
 				dfs(y);
 				ans.push_back(k);
 				
 			}
 		}
 	}
 }
 signed main(){
 	int i,x,y;
 	scanf("%d%d%d",&op,&n,&m);
 	
 	for(i=1;i<=m;i++){
 		x=read(),y=read();
 		
 		if(op==1){
 			add_(x,y),add_(y,x);
 			deg[x]++,deg[y]++;
 		}
 		else{
 			add_(x,y);
 			out[x]++,in[y]++;
 		}
 	}
 	if(op==1){
 		for(i=1;i<=n;i++)
 			if(deg[i]&1){ printf("NO\n"); return 0; }
 	}
 	else{
 		for(i=1;i<=n;i++){
 			if(in[i]!=out[i]){ printf("NO\n"); return 0; } 
 		}
 	}
 	
 	for(i=1;i<=n;i++){
 		if(hd[i]){ dfs(i); break; }
 	}
 	 
 	if(ans.size()==m){
 		cout<<"YES"<<endl;
 		for(i=ans.size()-1;i>=0;i--)  printf("%d ",ans[i]);
 	}
 	else{
 		cout<<"NO\n";
 	}	
 	
 }