Submission #256148

#	Time	Username	Problem	Language	Result	Execution time	Memory
256148		mode149256	Islands (IOI08_islands)	C++14	100 / 100	1182 ms	131072 KiB

islands

/*input

*/
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;

namespace my_template {
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;

typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef pair<ld, ld> pd;

typedef vector<int> vi;
typedef vector<vi> vii;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<vl> vll;
typedef vector<pi> vpi;
typedef vector<vpi> vpii;
typedef vector<pl> vpl;
typedef vector<cd> vcd;
typedef vector<pd> vpd;
typedef vector<bool> vb;
typedef vector<vb> vbb;
typedef std::string str;
typedef std::vector<str> vs;

#define x first
#define y second
#define debug(...) cout<<"["<<#__VA_ARGS__<<": "<<__VA_ARGS__<<"]\n"

const ld PI = 3.14159265358979323846264338327950288419716939937510582097494L;

template<typename T>
pair<T, T> operator+(const pair<T, T> &a, const pair<T, T> &b) { return pair<T, T>(a.x + b.x, a.y + b.y); }
template<typename T>
pair<T, T> operator-(const pair<T, T> &a, const pair<T, T> &b) { return pair<T, T>(a.x - b.x, a.y - b.y); }
template<typename T>
T operator*(const pair<T, T> &a, const pair<T, T> &b) { return (a.x * b.x + a.y * b.y); }
template<typename T>
T operator^(const pair<T, T> &a, const pair<T, T> &b) { return (a.x * b.y - a.y * b.x); }

template<typename T>
void print(vector<T> vec, string name = "") {
	cout << name;
	for (auto u : vec)
		cout << u << ' ';
	cout << '\n';
}
}
using namespace my_template;

const int MOD = 1000000007;
const ll INF = std::numeric_limits<ll>::max();
const int MX = 1000000;

int N;
vpi edges(MX);
vpii edgesVisos(MX);
vb been(MX, false);

vl circle; // lens
vi circleV;
vb inCircle(MX, false);

ll ats = 0;
ll proc = 0;
ll maxDis = 0;
int kur;

void fill(int x) {
	been[x] = true;

	for (auto u : edgesVisos[x])
		if (!been[u.x])
			fill(u.x);
}

// -1 ner rato
int find_circle(int x) {
	been[x] = true;

	auto u = edges[x];
	if (been[u.x]) {
		circleV.emplace_back(x);
		circle.emplace_back(u.y);
		been[x] = false;
		return u.x;
	}

	int k = find_circle(u.x);

	if (k == x) {
		circleV.emplace_back(x);
		circle.emplace_back(u.y);
		been[x] = false;
		return -1;
	}
	else if (k != -1) {
		circleV.emplace_back(x);
		circle.emplace_back(u.y);
		been[x] = false;
		return k;
	}

	been[x] = false;
	return -1;
}

void longest(int x, int p, ll dis) {
	if (dis > maxDis) {
		maxDis = dis;
		kur = x;
	}

	for (auto u : edgesVisos[x]) {
		if (u.x == p or inCircle[u.x]) continue;
		longest(u.x, x, dis + u.y);
	}
}

void solve() {
	proc = 0;
	for (auto u : circleV)
		inCircle[u] = true;

	int C = (int)circleV.size();

	vl D(C, 0);

	for (int i = 0; i < C; ++i)
	{
		int x = circleV[i];

		ll did = 0;
		ll did2 = 0;

		for (auto u : edgesVisos[x]) {
			if (inCircle[u.x]) continue;
			maxDis = 0;
			longest(u.x, x, u.y);
			proc = max(proc, maxDis);

			if (maxDis >= did) {
				did2 = did;
				did = maxDis;
			} else if (maxDis > did2) {
				did2 = maxDis;
			}


			D[i] = max(D[i], maxDis);

			maxDis = 0;
			longest(kur, -1, 0);
			proc = max(proc, maxDis);
		}

		proc = max(proc, did + did2);
	}

	deque<pl> dq;
	ll viso = 0;
	for (int i = 0; i < C; ++i) viso += circle[i];

	{
		for (int i = 1; i < C; ++i)
		{
			circle[i] += circle[i - 1];
			ll newVal = circle[i - 1] + D[i];

			while (dq.size() and dq.back().x <= newVal)
				dq.pop_back();

			dq.push_back({newVal, i});
		}

		for (int i = 0; i < C; ++i)
		{
			while (dq.size() and dq.front().y <= i) {
				dq.pop_front();
			}

			assert(dq.size());
			proc = max(proc, dq.front().x + D[i] - (i ? circle[i - 1] : 0));

			ll newVal = D[i] + viso + (i ? circle[i - 1] : 0);
			while (dq.size() and dq.back().x <= newVal)
				dq.pop_back();

			dq.push_back({newVal, i + C});
		}
	}

	ats += proc;
}

int main() {
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	cin >> N;
	for (int i = 0; i < N; ++i)
	{
		int a, w;
		cin >> a >> w; a--;

		edges[i] = {a, w};

		edgesVisos[i].emplace_back(a, w);
		edgesVisos[a].emplace_back(i, w);
	}


	for (int i = 0; i < N; ++i)
	{
		if (been[i]) continue;

		circle.clear();
		circleV.clear();

		find_circle(i);
		fill(i);
		reverse(circle.begin(), circle.end());
		reverse(circleV.begin(), circleV.end());

		solve();
	}

	printf("%lld\n", ats);
}

/* Look for:
* special cases (n=1?)
* overflow (ll vs int?)
* the exact constraints (multiple sets are too slow for n=10^6 :( )
* array bounds
*/

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 10 / 10