Submission #809061

#	Time	Username	Problem	Language	Result	Execution time	Memory
809061		Boomyday	Linear Garden (IOI08_linear_garden)	C++17	100 / 100	110 ms	3340 KiB

linear_garden

//
// Created by adavy on 2/11/2023.
//
#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using db = double;
using str = string; // yay python!

using ii = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;

using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vii = vector<ii>;
using vpl = vector<pl>;
using vpd = vector<pd>;

#define tcT template<class T
#define tcTU tcT, class U

tcT> using V = vector<T>;
tcT, size_t SZ> using AR = array<T,SZ>;
tcT> using PR = pair<T,T>;

// pairs
#define mp make_pair
#define f first
#define s second

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

#define len(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front

int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5;
const ll INF = 1e18; // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1,0,-1,0}, dy[4] = {0,1,0,-1}; // for every grid problem!!


struct Modular {
    int value;
    int MOD_value = MOD;

    Modular(long long v = 0) { value = v % MOD; if (value < 0) value += MOD;}
    Modular(long long a, long long b) : value(0){ *this += a; *this /= b;}

    Modular& operator+=(Modular const& b) {value += b.value; if (value >= MOD) value -= MOD; return *this;}
    Modular& operator-=(Modular const& b) {value -= b.value; if (value < 0) value += MOD;return *this;}
    Modular& operator*=(Modular const& b) {value = (long long)value * b.value % MOD;return *this;}

    friend Modular mexp(Modular a, long long e);
    friend Modular inverse(Modular a) { return mexp(a, MOD - 2); }

    Modular& operator/=(Modular const& b) { return *this *= inverse(b); }
    friend Modular operator+(Modular a, Modular const b) { return a += b; }
    friend Modular operator-(Modular a, Modular const b) { return a -= b; }
    friend Modular operator-(Modular const a) { return 0 - a; }
    friend Modular operator*(Modular a, Modular const b) { return a *= b; }
    friend Modular operator/(Modular a, Modular const b) { return a /= b; }
    friend std::ostream& operator<<(std::ostream& os, Modular const& a) {return os << a.value;}
    friend bool operator==(Modular const& a, Modular const& b) {return a.value == b.value;}
    friend bool operator!=(Modular const& a, Modular const& b) {return a.value != b.value;}
};

Modular mexp(Modular a, long long e) {
    Modular res = 1; while (e) { if (e&1) res *= a; a *= a; e >>= 1; }
    return res;
}



Modular numPaths(int pos, int botGone, int topGone, int movesLeft){

    if ((topGone-botGone)>=3) return 0;
    if ((topGone - botGone) == 2) {
        if (pos==topGone||pos==botGone) return mexp(2,movesLeft/2);
        else return mexp(2,(movesLeft+1)/2);

    }
    if (topGone-botGone==1) {
        return mexp(2,(movesLeft+1)/2) + mexp(2,movesLeft/2) - 1;
    }
    else return mexp(2,(movesLeft+1)/2) + 2*mexp(2,movesLeft/2) - 2;

}

int main(){
    int N, M; string S;
    cin >> N >> M;
    cin >> S;

    MOD = M;


    int pos=0, botGone=0, topGone=0,movesLeft = N;
    Modular gardNum = 0;

    F0R(i,N){
        movesLeft--;
        if (S[i]=='L'){
            // dont move
            pos++;
            topGone = max(pos,topGone);
        }
        else {
            gardNum += numPaths(pos+1,botGone,max(pos+1,topGone),movesLeft);
            pos--;
            botGone = min(pos,botGone);
        }
    }
    cout << gardNum+1 << endl;


}

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