Submission #229475

#	Time	Username	Problem	Language	Result	Execution time	Memory
229475		apostoldaniel854	Linear Garden (IOI08_linear_garden)	C++14	2 / 100	30 ms	3356 KiB

linear_garden

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
#define pb push_back
#define dbg(x) cerr << #x << " " << x << "\n"

int MOD;

int dp[2][2 + 2 + 1][2];

void _ (int &a, int b) {
    a += b;
    if (a >= MOD)
        a -= MOD;
}

int main() {
    ios::sync_with_stdio (false);
    cin.tie (0); cout.tie (0);

    int n;
    string garden;
    cin >> n >> MOD;
    cin >> garden; garden = " " + garden;
    /// -> L +1
    /// -> P -1
    if (garden[1] == 'L') {
        dp[1][2 + 1][1] = 1; /// put L as first element
    }
    else {
        dp[1][2 - 1][1] = 1; /// put P as first element
        dp[1][2 + 1][0] = 1; /// put L as first element, now we can put anything
    }
    for (int i = 2; i <= n; i++) {
        int cur = i & 1;
        int lst = !cur;
        for (int dif = -2; dif <= 2; dif++)
            for (int p = 0; p < 2; p++)
                dp[cur][2 + dif][p] = 0;
        for (int dif = -2; dif <= 2; dif++) {
            /// without prefix
            if (dif > -2)
                _ (dp[cur][2 + dif][0], dp[lst][2 + dif - 1][0]); /// add L
            if (dif < 2)
                _ (dp[cur][2 + dif][0], dp[lst][2 + dif + 1][0]); /// add P
            /// with prefix
            if (garden[i] == 'P') {
                if (dif > -2)
                    _ (dp[cur][2 + dif][0], dp[lst][2 + dif - 1][1]); /// add L so we get rid of prefix
                if (dif < 2)
                    _ (dp[cur][2 + dif][1], dp[lst][2 + dif + 1][1]); /// add P to continue prefix
            }
            else {
                if (dif > -2)
                    _ (dp[cur][2 + dif][1], dp[lst][2 + dif - 1][1]); /// add L to continue prefix
            }
        }
    }
    int ans = 0;
    for (int dif = -2; dif <= 2; dif++)
        for (int p = 0; p < 2; p++)
            _ (ans, dp[n & 1][2 + dif][p]);
    cout << ans << "\n";

    return 0;
}

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