NYOJ 一笔画

# include<iostream>
# include<string>
# include<string.h>
# include<queue>
# include<stdio.h>
# include<math.h>
#include <algorithm>
using namespace std;
#define MAX 4005
int first[MAX],next[MAX],u[MAX],v[MAX],used[MAX],h=,in[MAX];
//int out[MAX];
void AddEdge(int a,int b)
{
    u[h] = a;
    v[h] = b;
    if(h%==)
    {
        in[a]++;
        //out[a]++;
        in[b]++;
        //out[b]++;
    }
    next[h] = first[u[h]];
    first[u[h]] = h;
    h++;
}
int judge(int p)
{
    int count = ;
    int vertex[];
    for(int i=;i<=p;i++)
    {
        if(in[i] %  == )
        {
            if(count>=)
                return -;
            vertex[count] = i;
            count ++;
        }
    }
    if(count==)
    {
        return ;
    }
    else if(count == )
    {
        return -;
    }
    else if(count == )
    {
        return vertex[];
    }
    else
        return -;
}
void dfs(int k)        //k是出发顶点
{
    //printf("%d\n------------------\n",first[k]);
    if(first[k]==-)    //不存在以k为顶点的边
        return;
    else
    {
        k = first[k];
        while(k != -)
        {
            if(used[k]!=)
            {
                used[k] = ;
                if(k%==)
                    used[k+] = ;
                else
                {
                    used[k-] = ;
                }
                dfs(v[k]);
            }
            k = next[k];
        }
    }

}
int main()
{
    int m,n,i,j;
    cin>>n;
    while(n--)
    {
        int p,q;
        cin>>p>>q;
        h = ;
        for(i=;i<MAX;i++)
        {
            first[i] = -;
            next[i] = -;
            used[i] = ;
            in[i] = ;
            //out[i] = 0;
        }
        for(i=;i<=q;i++)
        {
            int a,b;
            scanf("%d %d",&a,&b);
            AddEdge(a,b);
            AddEdge(b,a);
        }

        int k,flag = ;
        k = judge(p);    //k为起点
        if(k==-)
        {
            printf("No\n");
            continue;
        }
        //printf("%d\n------------------\n",k);
        dfs(k);    //从起点开始寻找是否存在欧拉路 

        /******
        for(i=1;i<=h;i++)
        {
            k = first[i];
            while(k!=-1)
            {
                printf("%d %d %d %d %d\n",u[k],v[k],used[k],first[k],next[k]);
                k = next[k];
            }
        }
        *******/

        for(i=;i<h;i++)
        {
            if(used[i]!=)        //有边尚未访问 故不能一笔画
            {
                //printf("kk");
                flag = ;
                break;
            }
        }
        if(flag==)    printf("Yes\n");
        else        printf("No\n");
    }
    return ;
}