More than 2019 cattle off summer school camp (fifth) E.independent set 1 (like pressure dp)

Meaning of the questions: give you n points m edges ask largest independent set of all sub-graph and you

Ideas: we can set f state is the size of the current largest independent set in a set of points so we can put the set into two parts it contains this absolutely is absolutely a point that does not contain this point over and over again and then a maximum of two cases

Because of the open space is tight we have to use an array of char

#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
const int N = 1e5+7;
const int inf = 0x3f3f3f3f;
const double eps = 1e-6;
typedef long long ll;
const ll mod = 1e7+9;
int e[27];
char f[1<<26];
char max(char a,char b){
    if(a>b) return a;
    else return b;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    int n,m; cin>>n>>m;
    for(int i=1;i<=m;i++){
        int a,b; cin>>a>>b;
        e[a]=(e[a]|(1<<b));
        e[b]=(e[b]|(1<<a));
    }
    for(int i=0;i<n;i++){
        e[i]=(e[i]|(1<<i));
        e[i]=(~e[i]);
    }
    ll ans=0;
    f[0]=0;
    for(int i=1;i<(1<<n);i++){
        int po;
        for(int j=0;j<26;j++)
            if((i>>j)&1){
                po=j;
                break;
            }
        f[i]=max(f[i^(1<<po)],f[(i&e[po])]+1);
        ans+=f[i];
    }
    cout<<ans<<endl;
}