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#10108. 「一本通 3.7 练习 2」Ant Trip

无向图一笔画需要多少次（欧拉路径的条数）

答案：奇数点的个数 / 2

这题需要维护联通块，用并查集即可

#include <iostream>
#include <algorithm>
#include <cstring>
#include <stack>
using namespace std ;
  const int N=2e5+3,M=N;
   
 int all,nxt[M],go[N],hd[N];
 int n,m;
  
 void add_(int x,int y){
    nxt[++all]=hd[x]; hd[x]=all;
    go[all]=y;
 }
   
  int fa[N],deg[N],odd[N];
   
  int find(int x){
    return x==fa[x]?x:fa[x]=find(fa[x]);
  }
 signed main(){
    int i,x,y;
    while(cin>>n>>m){
        for(i=1;i<=n;i++) hd[i]=deg[i]=odd[i]=0,fa[i]=i; all=0;
         
        for(i=1;i<=m;i++){
            cin>>x>>y,add_(x,y),add_(y,x);
            deg[x]++,deg[y]++;
             
            int fx=find(x),fy=find(y);
            if(fx!=fy)
                fa[fy]=fx;
        }
        for(i=1;i<=n;i++){
            fa[i]=find(i);
            if(deg[i]&1) odd[fa[i]]++;
        }
        int ans=0;
        for(i=1;i<=n;i++) 
         if(fa[i]==i){
            if(deg[i]==0) continue; //
            if(odd[i]==0) ans++;
            else ans+=odd[i]/2;
         }
          
         cout<<ans<<endl;
    }
 }