Submission #776826

#	Time	Username	Problem	Language	Result	Execution time	Memory
776826		SanguineChameleon	Thousands Islands (IOI22_islands)	C++17	57.10 / 100	104 ms	19956 KiB

islands

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

const int maxN = 1e5 + 20;
vector<pair<int, int>> adj1[maxN];
vector<pair<int, int>> adj2[maxN];
pair<int, int> nxt[maxN];
pair<int, int> prv[maxN];
int deg[maxN];
bool rem[maxN];

variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
	for (int i = 0; i < M; i++) {
		adj1[U[i]].emplace_back(V[i], i);
		adj2[V[i]].emplace_back(U[i], i);
		deg[U[i]]++;
	}
	deque<int> Q;
	for (int i = 0; i < N; i++) {
		if (deg[i] == 0) {
			rem[i] = true;
			Q.push_back(i);
		}
	}
	vector<int> res;
	int start = 0;
	pair<int, int> nxt1, nxt2;
	while (true) {
		while (!Q.empty()) {
			int u = Q.front();
			Q.pop_front();
			for (auto e: adj2[u]) {
				int v = e.first;
				if (rem[v]) {
					continue;
				}
				deg[v]--;
				if (deg[v] == 0) {
					rem[v] = true;
					Q.push_back(v);
				}
			}
		}
		if (rem[start]) {
			return false;
		}
		nxt1 = {-1, -1};
		nxt2 = {-1, -1};
		for (auto e: adj1[start]) {
			if (!rem[e.first]) {
				if (nxt1.first == -1) {
					nxt1 = e;
				}
				else if (nxt2.first == -1) {
					nxt2 = e;
				}
			}
		}
		if (nxt1.first == -1) {
			return false;
		}
		if (nxt2.first == -1) {
			rem[start] = true;
			Q.push_back(start);
			start = nxt1.first;
			res.push_back(nxt1.second);
		}
		else {
			break;
		}
	}
	for (int i = 0; i < N; i++) {
		if (rem[i] || i == start) {
			continue;
		}
		for (auto e: adj1[i]) {
			if (!rem[e.first]) {
				nxt[i] = e;
				break;
			}
		}
	}
	bool has_start = false;
	bool done = false;
	for (int iter = -1; iter < 4; iter++) {
		for (int i = 0; i < N; i++) {
			prv[i] = {-1, -1};
		}
		int u = -1;
		int extra = -1;
		if (iter == 1 && has_start) {
			extra = nxt2.second;
			u = nxt2.first;
			prv[nxt2.first] = {nxt2.first, -1};
		}
		else {
			if (iter != 2 || !has_start) {
				nxt[start] = (iter == -1 ? nxt2 : ((iter & 1) ? nxt2 : nxt1));
			}
			u = start;
			prv[start] = {start, -1};
		}
		while (true) {
			int v = nxt[u].first;
			if (prv[v].first != -1) {
				if (iter == -1) {
					if (v == start) {
						swap(nxt1, nxt2);
					}
					break;
				}
				nxt[v] = {u, nxt[u].second};
				vector<int> cycle = {nxt[u].second};
				while (u != v) {
					if (iter == 1) {
						done |= (u == start);
					}
					cycle.push_back(prv[u].second);
					nxt[u] = prv[u];
					u = prv[u].first;
				}
				if (iter == 1) {
					done |= (u == start);
				}
				vector<int> suf;
				while (u != ((iter == 1 && has_start) ? nxt2.first : start)) {
					suf.push_back(prv[u].second);
					u = prv[u].first;
				}
				if (iter == 1 && has_start) {
					suf.push_back(extra);
				}
				res.insert(res.end(), suf.rbegin(), suf.rend());
				res.insert(res.end(), cycle.rbegin(), cycle.rend());
				res.insert(res.end(), suf.begin(), suf.end());
				if (iter == 0) {
					has_start = (v == start);
				}
				break;
			}
			else {
				prv[v] = {u, nxt[u].second};
				u = v;
			}
		}
		if (iter == 1 && has_start && done) {
			break;
		}
	}
	return res;
}

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 24 / 24
• Subtask 5: 15.749999999999998 / 45