AcWing 1184欧拉回路（打板子踩坑记）

#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;

const int Maxn = 2e5 + 10;
bool visit[Maxn*2 + 100];
int fa[Maxn];
int indegree[Maxn];
int outdegree[Maxn];
int ans[Maxn];
int cur;
int Next[Maxn];

struct Edge{
    int v;
    int id;
    
    Edge(int v, int id) : v(v), id(id) {}
};

vector<vector<Edge> > G(Maxn);
int T;

int find(int x)
{
    return x == fa[x] ? x : fa[x] = find(fa[x]);
}

bool issame(int a, int b)
{
    return find(a) == find(b);
}

void unite(int a, int b)
{
    if(!issame(a, b)){
        fa[find(a)] = find(b);
    }
}

bool isOK(int n)
{
    int pre = -1;
    if(T == 1){
        for(int i=1; i<=n ;i++){
            if(pre != find(i) && G[i].size() != 0){
                if(pre == -1) pre = find(i);
                else return false;
            }
            
            if(indegree[i] & 1) return false;
        }
    }
    else if(T == 2){
        for(int i=1; i<=n ;i++){
            if(pre != find(i) && G[i].size() != 0){
                if(pre == -1) pre = find(i);
                else return false;
            }
            
            if(indegree[i] != outdegree[i]) return false;
        }
    }
    
    return true;
}

void dfs(int x, int pre)
{
    for(int i=Next[x]; i<G[x].size() ;i++){
        int v = G[x][i].v;
        int id = G[x][i].id;
        Next[x] = i+1;
        int pre = Next[x];
        if(visit[abs(id)]) continue;
        
        visit[abs(id)] = true;
        dfs(v, id);
        if(pre != Next[x]) break;
    }
    
    if(pre != 0) ans[cur++] = pre;
}

int main()
{
    cin>>T;
    int n, m;
    cin>>n>>m;
    for(int i=1; i<=n ;i++)
        fa[i] = i;
    
    int start = 1;
    for(int i=1; i<=m ;i++){
        int u, v;
        cin>>u>>v;
        start = u;
        if(T == 1){
            G[u].push_back(Edge(v, i));
            G[v].push_back(Edge(u, -i));
            indegree[u]++;
            indegree[v]++;
            outdegree[u]++;
            outdegree[v]++;
        }
        else{
            G[u].push_back(Edge(v, i));
            outdegree[u]++;
            indegree[v]++;
        }
        
        unite(u, v);
    }
    
    if(!isOK(n)) cout<<"NO";
    else{
        cout<<"YES"<<endl;
        
        dfs(start, 0);
        for(int i=cur-1; i>=0 ;i--)
            cout<<ans[i]<<" ";
    }
    
    return 0;
}