Problem - 691E - Codeforces

题意：

思路：

有人只会暴力DP忘记矩阵快速幂怎么写了

 

 

Code：

#include <bits/stdc++.h>

#define int long long

using i64 = long long;

using namespace std;

const int N = 1e2 + 10;
const int mod = 1e9 + 7;

int n, k;
int a[N];

struct Matrix {
    int m[N][N];
    void init() {
        for (int i = 1; i <= n; i ++) {
            m[i][i] = 1;
        }
    }
    void clr() {
        for (int i = 1; i <= n; i ++) {
            for (int j = 1; j <= n; j ++) {
                m[i][j] = 0;
            }
        }
    }
};

Matrix Mul(Matrix a, Matrix b) {
    Matrix ans;
    ans.clr();
    for (int i = 1; i <= n; i ++) {
        for (int j = 1; j <= n; j ++) {
            for (int k = 1; k <= n; k ++) {
                ans.m[i][j] += a.m[i][k] * b.m[k][j];
                ans.m[i][j] %= mod;
            }
        }
    }
    return ans;
}

Matrix ksm(Matrix a, int b) {
    Matrix res;
    res.clr();
    res.init();
    while(b) {
        if (b & 1) res = Mul(res, a);
        a = Mul(a, a);
        b >>= 1;
    }
    return res;
}

void solve() {
    cin >> n >> k;
    for (int i = 1; i <= n ;i ++) {
        cin >> a[i];
    }

    Matrix Base;
    Base.clr();
    for (int i = 1; i <= n; i ++) {
        for (int j = 1; j <= n; j ++) {
            if (__builtin_popcountll(a[i] ^ a[j]) % 3 == 0) {
                Base.m[i][j] = 1;
            }
        }
    }

    Base = ksm(Base, k - 1);
    int ans = 0;
    for (int i = 1; i <= n; i ++) {
        for (int j = 1; j <= n; j ++) {
            ans += Base.m[i][j];
            ans %= mod;
        }
    }
    cout << ans << "\n";
}
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t = 1;
    //cin >> t;
    while(t --) {
        solve();
    }
    return 0;
}