CodeForces 723E One-Way Reform

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<ctime>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0),eps=1e-10;
void File()
{
    freopen("D:\\in.txt","r",stdin);
    freopen("D:\\out.txt","w",stdout);
}
template <class T>
inline void read(T &x)
{
    char c = getchar();
    x = 0;
    while(!isdigit(c)) c = getchar();
    while(isdigit(c))
    {
        x = x * 10 + c - ‘0‘;
        c = getchar();
    }
}

int T,n,m,ans,cnt;
vector<int>v[210];
int f[210];
int ss[100000],ee[100000],t[210][210],p[210][210];

void dfs(int x)
{
    for(int i=v[x].size()-1;i>=0;i--)
    {
        if(t[x][v[x][i]]==1) continue;

        t[x][v[x][i]]=t[v[x][i]][x]=1;
        ss[cnt]=x; ee[cnt]=v[x][i]; cnt++;

        dfs(v[x][i]);
    }
}

int main()
{
    cin>>T;
    for(int cas=1;cas<=T;cas++)
    {
        cin>>n>>m;

        for(int i=1;i<=n+1;i++) v[i].clear();

        memset(f,0,sizeof f);
        memset(p,0,sizeof p);

        for(int i=1;i<=m;i++)
        {
            int a,b; cin>>a>>b;

            v[a].push_back(b);
            v[b].push_back(a);
            f[a]++; f[b]++;
            p[a][b]=p[b][a]=1;
        }

        ans=0; vector<int>x;
        for(int i=1;i<=n;i++)
        {
            if(f[i]%2==0) ans++;
            else x.push_back(i);
        }

        for(int i=0;i<x.size();i++)
        {
            v[n+1].push_back(x[i]);
            v[x[i]].push_back(n+1);
        }

        memset(t,0,sizeof t); cnt=0;
        for(int i=1;i<=n+1;i++) dfs(i);

        printf("%d\n",ans);

        for(int i=0;i<m+(n-ans);i++)
        {
            if(p[ss[i]][ee[i]]==1)
                printf("%d %d\n",ss[i],ee[i]);
        }

    }
    return 0;
}