• 奇(qi)谋(ji)巧(yin)计(qiao)


    一、打表法

    0.http://oeis.org/

    1.差分序列:https://blog.csdn.net/wu_tongtong/article/details/79115921

    对于一个多项式产生的序列,可以多次求差分序列,直到差分序列均为0,这时原序列的表达式就可以表示为:

    其中,c0……cp为差分表的第0条对角线。

    同时有求和公式

    确定有公式后除去可以确定的项

    #include <bits/stdc++.h>
    
    using namespace std;
    #define rep(i, a, n) for (ll i=a;i<n;i++)
    #define SZ(x) ((ll)(x).size())
    typedef long long ll;
    const ll mod = 1000000007;
    
    ll powmod(ll a, ll b) {
        ll res = 1;
        a %= mod;
        for (; b; b >>= 1) {
            if (b & 1)res = res * a % mod;
            a = a * a % mod;
        }
        return res;
    }
    
    ll n;
    namespace linear_seq {
        const ll N = 100010;
        ll res[N], base[N], _c[N], _md[N];
    
        vector<ll> Md;
    
        void mul(ll *a, const ll *b, ll k) {
            rep(i, 0, k + k) _c[i] = 0;
            rep(i, 0, k) if (a[i]) rep(j, 0, k) _c[i + j] = (_c[i + j] + a[i] * b[j]) % mod;
            for (ll i = k + k - 1; i >= k; i--)
                if (_c[i])
                    rep(j, 0, SZ(Md)) _c[i - k + Md[j]] = (_c[i - k + Md[j]] - _c[i] * _md[Md[j]]) % mod;
            rep(i, 0, k) a[i] = _c[i];
        }
    
        ll solve(ll n, vector<ll> a, vector<ll> b) {
            ll ans = 0, pnt = 0;
            ll k = SZ(a);
            rep(i, 0, k) _md[k - 1 - i] = -a[i];
            _md[k] = 1;
            Md.clear();
            rep(i, 0, k) if (_md[i] != 0) Md.push_back(i);
            rep(i, 0, k) res[i] = base[i] = 0;
            res[0] = 1;
            while (1ll << pnt <= n) pnt++;
            for (ll p = pnt; p >= 0; p--) {
                mul(res, res, k);
                if (n >> p & 1) {
                    for (ll i = k - 1; i >= 0; i--) res[i + 1] = res[i];
                    res[0] = 0;
                    rep(j, 0, SZ(Md)) res[Md[j]] = (res[Md[j]] - res[k] * _md[Md[j]]) % mod;
                }
            }
            rep(i, 0, k) ans = (ans + res[i] * b[i]) % mod;
            if (ans < 0) ans += mod;
            return ans;
        }
    
        vector<ll> BM(vector<ll> s) {
            vector<ll> C(1, 1), B(1, 1);
            ll L = 0, m = 1, b = 1;
            rep(n, 0, SZ(s)) {
                ll d = 0;
                rep(i, 0, L + 1) d = (d + (ll) C[i] * s[n - i]) % mod;
                if (d == 0) ++m;
                else if (2 * L <= n) {
                    vector<ll> T = C;
                    ll c = mod - d * powmod(b, mod - 2) % mod;
                    while (SZ(C) < SZ(B) + m) C.push_back(0);
                    rep(i, 0, SZ(B)) C[i + m] = (C[i + m] + c * B[i]) % mod;
                    L = n + 1 - L;
                    B = T;
                    b = d;
                    m = 1;
                } else {
                    ll c = mod - d * powmod(b, mod - 2) % mod;
                    while (SZ(C) < SZ(B) + m) C.push_back(0);
                    rep(i, 0, SZ(B)) C[i + m] = (C[i + m] + c * B[i]) % mod;
                    ++m;
                }
            }
            return C;
        }
    
        vector<ll> temp;
    
        void init(vector<ll> a) {
            temp = BM(a);
            temp.erase(temp.begin());
            rep(i, 0, SZ(temp))temp[i] = (mod - temp[i]) % mod;
        }
    
        ll gao(vector<ll> a, ll n) {
            return solve(n, temp, vector<ll>(a.begin(), a.begin() + SZ(temp)));
        }
    };
    using namespace linear_seq;
    
    int main() {
    
        vector<ll> v;
        v.push_back(3);
        v.push_back(9);
        v.push_back(20);
        v.push_back(46);
        v.push_back(106);
        v.push_back(244);
        v.push_back(560);
        v.push_back(1286);
        v.push_back(2956);
        v.push_back(6794);
        init(v);
        ll T;
        scanf("%lld", &T);
        while (T--) {
            ll n;
            scanf("%lld", &n);
            printf("%lld
    ", gao(v, n - 1));
        }
        return 0;
    }
    递推
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  • 原文地址:https://www.cnblogs.com/bestefforts/p/9486576.html
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