Submission #1248318

#	Time	Username	Problem	Language	Result	Execution time	Memory
1248318		Lithanium	Linear Garden (IOI08_linear_garden)	C++20	95 / 100	164 ms	78808 KiB

linear_garden

#include <bits/stdc++.h>
using namespace std;

bitset<1000005> num;
int dp[1000005][2][2];
int N, M;

int solve(int n, char L, char P, bool lim) {
    if (L > 2 or P > 2) return 0;
    if (n == N) return 1;
    if (!lim and max(L, P) < 2 and dp[n][L][P] != -1) return dp[n][L][P];
    int top = 1;
    if (lim and num[n+1] == 0) top = 0;
    int ans = 0;
    // put a 0
    if (L != 2) (ans += solve(n+1, L+1, max(0, P-1), lim and (top == 0))) %= M;
    // put a 1
    if (top and P != 2) (ans += solve(n+1, max(0, L-1), P+1, lim)) %= M;
    if (!lim and max(L, P) < 2) return dp[n][L][P] = ans;
    return ans;
}

int main() {
    memset(dp, -1, sizeof(dp));
    cin >> N >> M;
    for (int i = 1; i <= N; i ++) {
        char c;
        cin >> c;
        if (c == 'P') num[i] = 1;
    }
    cout << solve(0, 0, 0, 1);
}

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