poj 1419 Graph Coloring

#include<cstdio>
#include<cstring>
#include<iostream>

using namespace std;

bool map[101][101];
int color[101],res[101];

int n,ans,cnt;

void read(int &x)
{
    x=0; char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) { x=x*10+c-‘0‘; c=getchar(); }
}

bool can(int s)
{
    for(int i=1;i<=n;++i)
    {
        if(map[s][i] && color[i]==1) return false;
    }
    return true;
}

void dfs(int p)
{
    if(p>n)
    {
        ans=cnt;
        int k=0;
        for(int i=1;i<=n;++i)
        {
            if(color[i]==1) res[++k]=i;
        }
        return;
    }
    if(cnt+n-p+1<=ans) return;
    if(can(p))
    {
        cnt++;
        color[p]=1;
        dfs(p+1);
        cnt--;
    }
    color[p]=2;
    dfs(p+1);
}

int main()
{
    int T;
    read(T);
    int m,x,y;
    while(T--)
    {
        read(n); read(m);
        memset(map,false,sizeof(map));
        memset(color,0,sizeof(color));
        while(m--)
        {
            read(x); read(y);
            map[x][y]=map[y][x]=true;
        }
        ans=cnt=0;
        dfs(1);
        cout<<ans<<‘\n‘;
        for(int i=1;i<ans;++i) cout<<res[i]<<‘ ‘;
        cout<<res[ans]<<‘\n‘;
    }
}