Submission #310419

#	Time	Username	Problem	Language	Result	Execution time	Memory
310419		Temmie	Linear Garden (IOI08_linear_garden)	C++17	86 / 100	121 ms	2460 KiB

linear_garden

#include <bits/stdc++.h>

typedef long long ll;

ll pow(ll x, ll p, ll m) {
	p %= m;
	ll r = 1;
	while (p) {
		if (p & 1LL) r = (r * x) % m;
		x = (x * x) % m;
		p >>= 1LL;
	}
	return r;
}

ll rem(ll& x, ll m) {
	x--;
	if (x == -1LL) x += m;
	return x;
}

int main() {
	std::ios::sync_with_stdio(0); std::cin.tie(0);
	
	ll n, m; std::cin >> n >> m;
	std::string s; std::cin >> s;
	ll l = 0, r = 0, now = 0, ans = 0;
	for (ll i = 0; i < n; i++) {
		if (s[i] == 'L') now++, r = std::max(r, now);
		else {
			ll rr = std::max(r, now + 1LL);
			ll rn = n - i - 1LL;
			if (!(rr - l - 1LL)) ans = (ans + pow(2LL, rn >> 1LL, m) + pow(2LL, (rn + 1LL) >> 1LL, m)) % m, rem(ans, m);
			else if (!(rr - l - 2)) {
				if (now + 1LL == rr - 1LL) ans = (ans + pow(2LL, (rn + 1LL) >> 1LL, m)) % m;
				else ans = (ans + pow(2LL, rn >> 1LL, m)) % m;
			}
			now--, l = std::min(l, now);
		}
	}
	std::cout << (ans + 1LL) % m << "\n";
	
}

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