Submission #3768126

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Source Code Expand

#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(auto& (a): (b))
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define spair(p) cout<<#p<<": "<<p.fi<<" "<<p.se<<endl
#define sar(a,n) cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl
#define svec(v) cout<<#v<<":";rep(pachico,v.size())cout<<" "<<v[pachico];cout<<endl
#define svecp(v) cout<<#v<<":";each(pachico,v)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl
#define sset(s) cout<<#s<<":";each(pachico,s)cout<<" "<<pachico;cout<<endl
#define smap(m) cout<<#m<<":";each(pachico,m)cout<<" {"<<pachico.first<<":"<<pachico.second<<"}";cout<<endl

using namespace std;

typedef pair<int,int> P;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 500;

int n,m;

template <int COL_SIZE> class mat {
private:
    // (or, and) の意味での積(正方かつ対称行列に限る(重みなし無向グラフの隣接行列とか))
    mat operator*(const mat& m) const {
        mat ans;
        for(int i = 0; i < COL_SIZE; i++){
            for(int j = 0; j < COL_SIZE; j++){
                if(this->a[i][j] == 0) continue;
                ans.a[i] |= m.a[j];
            }
        }
        return ans;
    }
    
public:
    bitset<COL_SIZE>* a;
    int r;
    // 正方行列の場合
    mat(){ a = new bitset<COL_SIZE>[COL_SIZE]; }
    // 一般の行列の場合
    mat(int row_size) : r(row_size){ a = new bitset<COL_SIZE>[r]; }
    int rank() const {
        int res = 0;
        mat<COL_SIZE> b(r);
        for(int i = 0; i < r; i++) b[i] = a[i];
        for(int i = 0; i < COL_SIZE; i++){
            if(res == r) return res;
            int pivot = res;
            if(!b[pivot][i]){
                for(int j = res + 1; j < r; j++){
                    if(b[j][i]){
                        pivot = j;
                        break;
                    }
                }
                if(!b[pivot][i]) continue;
                swap(b[pivot], b[res]);
            }
            for(int j = res + 1; j < r; j++){
                if(b[j][i]) b[j] ^= b[res];
            }
            res++;
        }
        return res;
    }
    inline const bitset<COL_SIZE>& operator[](size_t index) const {
        return a[index];
    }
    inline bitset<COL_SIZE>& operator[](size_t index){
        return a[index];
    }
    friend mat pow(mat m, long long cnt){
        mat res;
        for(int i = 0; i < COL_SIZE; i++) res[i][i] = 1;
        while(cnt){
            if(cnt & 1){
                res = res * m;
            }
            m = m * m;
            cnt >>= 1;
        }
        return res;
    }
};

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m;
    mat<MAX_N> A;
    rep(i,m){
        int x,y;
        cin >> x >> y;
        A[x-1][y-1] = 1;
    }
    ll l = 0, r = 50000000000LL;
    if((int)pow(A,r)[0].count() != n){
        cout << "-1\n";
        return 0;
    }
    while(r-l>1){
        ll mid = (l+r)/2;
        if((int)pow(A,mid)[0].count() == n){
            r = mid;
        }else{
            l = mid;
        }
    }
    cout << r%MOD << "\n";
    return 0;
}

Submission Info

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