Submission #924068

#	Time	Username	Problem	Language	Result	Execution time	Memory
924068		thinknoexit	Linear Garden (IOI08_linear_garden)	C++17	100 / 100	18 ms	9052 KiB

linear_garden

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 1000001;
/*
    L +
    P -
    [0, 2]
    [-1, 1]
    [-2, 0]
*/
int pw[N], n, MOD;
int v[N];
int solve() {
    int ans = 0;
    int c = 0;
    for (int i = n;i >= 1;i--) {
        int idx = n - i + 1;
        int now = v[idx];
        if (now == 0) {
            c++;
        }
        else {
            if (c == 1) {
                ans = (ans + pw[(i - 1) / 2]) % MOD;
            }
            c--;
        }

    }
    return ans;
}
int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    cin >> n >> MOD;
    int c = 0, mn = 0;
    pw[0] = 1;
    for (int i = 1;i <= n;i++) {
        pw[i] = pw[i - 1] * 2 % MOD;
        char s;
        cin >> s;
        if (s == 'L') v[i] = 0, c++;
        else v[i] = 1, c--;
        mn = min(mn, c);
    }
    if (mn == 0) {
        cout << (solve() + 1) % MOD;
        return 0;
    }
    if (mn == -1) {
        int ans = pw[n / 2];
        c = 0;
        for (int i = n;i >= 1;i--) {
            int now = v[n - i + 1];
            if (now == 0) {
                c++;
            }
            else {
                if (c == 0) {
                    ans = (ans + pw[i / 2]) % MOD;
                }
                c--;
            }

        }
        cout << ans;
        return 0;
    }
    int all1 = (pw[n / 2] - 1 + MOD) % MOD;
    int ans = all1;
    ans = (ans + pw[(n + 1) / 2]) % MOD;
    for (int i = 1;i <= n;i++) v[i] ^= 1;
    cout << (ans + (all1 - solve() + MOD) % MOD) % MOD;
    return 0;
}

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