Submission #1320121

#TimeUsernameProblemLanguageResultExecution timeMemory
1320121nicolo_010Connecting Supertrees (IOI20_supertrees)C++20
40 / 100
125 ms22168 KiB
#include "supertrees.h"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;

struct DSU {
	vector<int> rank, parent;
	DSU(int n) {
		rank.assign(n, 1);
		parent.resize(n);
		for (int i=0; i<n; i++) {
			parent[i] = i;
		}
	}
	int find(int n) {
		return (n == parent[n] ? n : parent[n] = find(parent[n]));
	}
	void unite(int n1, int n2) {
		int p1 = find(n1);
		int p2 = find(n2);
		if (p1 == p2) return;
		rank[p1] += rank[p2];
		parent[p2] = p1;
	}
};

int construct(std::vector<std::vector<int>> p) {
	int n = p.size();
	vector<vector<int>> ans(n, vector<int>(n, 0));
	bool can = true;
	for (int i=0; i<n; i++) {
		for (int j=0; j<n; j++) {
			if (p[i][j] != p[j][i]) can = false;
		}
	}
	if (!can) {
		return 0;
	}
	DSU dsu(n);
	for (int i=0; i<n; i++) {
		for (int j=0; j<n; j++) {
			if (p[i][j] >= 1) dsu.unite(i, j);
		}
	}
	for (int i=0; i<n; i++) {
		int pi = dsu.find(i);
		if (pi == i) {
			//i es el root de su componente
			vector<int> cmp;
			for (int j=0; j<n; j++) {
				int pj = dsu.find(j);
				if (pi==pj) {
					cmp.push_back(j);
				}
			}
			//cmp tiene la componente completa
			vector<int> star; //Nodos en star son aquellos que deben formar una estrella;
			set<int> s;
			for (auto x : cmp) {
				for (auto y : cmp) {
					if (x==y) continue;
					if (p[x][y] == 1) {
						s.insert(x);
						s.insert(y);
					}
				}
			}
			star = vector<int>(s.begin(), s.end());
			if (star.size()>0) {
				int u = star[0];
				for (auto x : star) {
					ans[u][x] = ans[x][u] = 1;
				}
				//Formo estrella
			}
			vector<int> complement;
			for (auto x : cmp) {
				if (!s.count(x)) complement.push_back(x);
			}
			//Complement son aquellos nodos que estan en la componente pero no deben ser parte de la estrella.
			//Si hay estrella en la componente, uno de estos nodos debe estar conectado al ciclo.
			//Otherwise, el ciclo es toda la componente
			if (star.size()>0) complement.push_back(star[0]);
			int m = complement.size();
			for (int j=0; j<m; j++) {
				int u = complement[j];
				int v = complement[(j+1)%m];
				ans[u][v] = ans[v][u] = 1;
			}
			for (auto x : cmp) {
				for (auto y : cmp) {
					if (p[x][y] == 0) return 0;
				}
			}
			if (star.size()==0 && cmp.size()==2) return 0;
		}
	}
	for (int i=0; i<n; i++) {
		ans[i][i] = 0;
	}
	build(ans);
	return 1;
}
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