求欧拉回路

圈套圈。该模板是uoj那道题的。

//#include<iostream>
#include<cstring>
#include<cstdio>
#include<time.h>
//#include<math.h>
//#include<set>
#include<queue>
//#include<bitset>
//#include<vector>
#include<algorithm>
#include<stdlib.h>
using namespace std;

#define LL long long
LL qread()
{
    char c; LL s=0; int f=1; while ((c=getchar())<'0' || c>'9') (c=='-') && (f=-1);
    do s=s*10+c-'0'; while ((c=getchar())>='0' && c<='9'); return s*f;
}

//Pay attention to '-' , LL and double of qread!!!!

int n,t,m;
#define maxn 100011
#define maxm 400011
struct Edge{int to,next;}edge[maxm]; int first[maxn],le=2;
void in(int x,int y) {Edge &e=edge[le]; e.to=y; e.next=first[x]; first[x]=le++;}
void insert(int x,int y) {in(x,y); in(y,x);}

//int ufs[maxn],size[maxn];
//int find(int x) {return x==ufs[x]?x:(ufs[x]=find(ufs[x]));}
//void Union(int x,int y) {x=find(x); y=find(y); if (x!=y) ufs[x]=y,size[y]+=size[x];}

int du[maxn],indu[maxn],odu[maxn];

int sta[maxm],top=0,boss; bool vis[maxm];
void dfs(int x,int fa)
{
//    cout<<x<<endl;
    for (int &i=first[x];i;i=edge[i].next)
    {
        if ((i^1)==fa) continue;
        if (~fa && vis[i>>1]) continue;
        if (fa==-1 && vis[i]) continue;
        int j=i; Edge &e=edge[j]; if (~fa) vis[j>>1]=1; else vis[j]=1;
        if (e.to==boss) {if (~fa) sta[++top]=(j&1)?-(j>>1):(j>>1); else sta[++top]=j-1; boss=0; continue;}
        if (boss==0) x=boss;
        dfs(e.to,fa==-1?-1:j); if (~fa) sta[++top]=(j&1)?-(j>>1):(j>>1); else sta[++top]=j-1;
    }
}

void solve1()
{
    for (int i=1;i<=n;i++) if (du[i]&1) {puts("NO"); return;}
    for (int i=1;i<=n;i++) if (du[i]) {dfs((boss=i),0); break;}
    if (top!=m) {puts("NO"); return;}
    puts("YES");
    for (int i=top;i;i--) printf("%d ",sta[i]);
}

void solve2()
{
    for (int i=1;i<=n;i++) if (indu[i]!=odu[i]) {puts("NO"); return;}
    for (int i=1;i<=n;i++) if (indu[i]) {dfs((boss=i),-1); break;}
    if (top!=m) {puts("NO"); return;}
    puts("YES");
    for (int i=top;i;i--) printf("%d ",sta[i]);
}

int main()
{
    t=qread(); n=qread(); m=qread();
    if (m==0) {puts("YES"); return 0;}
    for (int i=1,x,y;i<=m;i++)
    {x=qread(); y=qread(); if (t==1) insert(x,y),du[x]++,du[y]++; else in(x,y),indu[y]++,odu[x]++;}
    if (t==1) solve1(); else solve2();
    return 0;
}

顺便加个题51nod1967 路径定向

这可以用网络流，但T死。

实际把奇数度数点连起来做欧拉回路就好了。