The 32nd International Olympiad in Informatics was held in Online in 2020. There were two competition days, with 3 tasks given to the competitors on each day. You can see Supertrees Problem and Solution below.
Problem :
day1-supertrees-ISCSolution :
#include "supertrees.h"
#include <bits/stdc++.h>
#define sz(v) ((int)(v).size())
#define all(v) (v).begin(), (v).end()
using namespace std;
using lint = long long;
using llf = long double;
const int MAXN = 1505;
struct disj{
int pa[MAXN];
int sz[MAXN];
void init(int n){
iota(pa, pa + n + 1, 0);
fill(sz, sz + n + 1, 1);
}
int find(int x){
return pa[x] = (pa[x] == x ? x : find(pa[x]));
}
int getsz(int x){ return sz[find(x)]; }
bool uni(int p, int q){
p = find(p);
q = find(q);
if(p == q) return 0;
sz[p] += sz[q];
pa[q] = p; return 1;
}
}disj, cx;
int n;
int construct(std::vector<std::vector<int>> a) {
n = sz(a);
disj.init(n);
std::vector<std::vector<int>> answer(n);
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
if(a[i][j] == 1) disj.uni(i, j);
if(a[i][j] == 3) return 0;
}
answer[i].resize(n);
}
vector<int> v;
for(int i=0; i<n; i++){
if(disj.find(i) != i){
answer[i][disj.find(i)] = 1;
answer[disj.find(i)][i] = 1;
}
else v.push_back(i);
}
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
if(a[i][j] != a[disj.find(i)][disj.find(j)]) return 0;
}
}
cx.init(n);
for(auto &i : v){
for(auto &j : v){
if(a[i][j] == 2){
cx.uni(i, j);
}
}
}
vector<int> v2[MAXN];
for(auto &i : v){
if(cx.getsz(i) > 1) v2[cx.find(i)].push_back(i);
}
for(int i=0; i<n; i++){
if(sz(v2[i]) && sz(v2[i]) <= 2) return 0;
for(auto &x : v2[i]){
for(auto &y : v2[i]){
if(x != y && a[x][y] != 2) return 0;
}
}
if(sz(v2[i])){
for(int j=0; j<sz(v2[i]); j++){
int l = v2[i][j];
int r = v2[i][(j+1)%sz(v2[i])];
answer[l][r] = answer[r][l] = 1;
}
}
}
disj.init(n);
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
if(answer[i][j]) disj.uni(i, j);
}
}
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
if(a[i][j] == 0 && disj.find(i) == disj.find(j)) return 0;
}
}
build(answer);
return 1;
}
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