| # | Time | Username | Problem | Language | Result | Execution time | Memory |
|---|---|---|---|---|---|---|---|
| 674073 | US3RN4M3 | Thousands Islands (IOI22_islands) | C++17 | 0 ms | 0 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include"islands.h"
#include<vector>
#include<algorithm>
#include<iostream>
using namespace std;
using ll = long long;
const int mx = 200005;
bool is_cycle[mx];
int N;
vector<pair<int, int>> graph[mx];
vector<pair<int, int>> bck[mx];
vector<vector<int>> groups;
int group_id[mx];
bool vis[mx];
vector<int> topo;
vector<int> ans;
int cur_group_id;
pair<int, int> par[mx];
void dfs(int cur) {
vis[cur] = true;
for(auto [nxt, id] : graph[cur]) if(!vis[nxt]) {
dfs(nxt);
}
topo.push_back(cur);
}
void dfs2(int cur) {
vis[cur] = true;
for(auto [prv, id] : bck[cur]) if(!vis[prv]) {
dfs2(prv);
}
group_id[cur] = cur_group_id;
groups.back().push_back(cur);
}
pair<int, int> cycle_next[mx];
bool test_cycle(int bit) {
ans.clear();
vector<int> tour1, tour2, cycle1, cycle2;
for(int _ = 0; _ < 2; _++) {
swap(tour1, tour2);
swap(cycle1, cycle2);
for(int i = 0; i < N; i++) vis[i] = false;
vector<int> q;
for(auto [nxt, id] : graph[0]) {
if(_ == 0) {
if((id >> bit) & 1) {
if(vis[nxt]) continue;
vis[nxt] = true;
q.push_back(nxt);
par[nxt] = {0, id};
}
} else {
if(!((id >> bit) & 1)) {
if(vis[nxt]) continue;
vis[nxt] = true;
q.push_back(nxt);
par[nxt] = {0, id};
}
}
}
int qidx = 0;
while(qidx < q.size()) {
int cur = q[qidx++];
if(is_cycle[cur]) {
int tmp = cur;
while(tmp != 0) {
tour1.push_back(par[tmp].second);
tmp = par[tmp].first;
}
reverse(tour1.begin(), tour1.end());
tmp = cur;
do {
cycle1.push_back(cycle_next[tmp].second);
tmp = cycle_next[tmp].first;
} while(tmp != cur);
break;
}
for(auto [nxt, id] : graph[cur]) {
if(vis[nxt]) continue;
par[nxt] = {cur, id};
vis[nxt] = true;
q.push_back(nxt);
}
}
}
if(cycle1.size() == 0) return false;
if(cycle2.size() == 0) return false;
vector<int> tour1r = tour1;
vector<int> tour2r = tour2;
vector<int> cycle1r = cycle1;
vector<int> cycle2r = cycle2;
reverse(tour1r.begin(), tour1r.end());
reverse(tour2r.begin(), tour2r.end());
reverse(cycle1r.begin(), cycle1r.end());
reverse(cycle2r.begin(), cycle2r.end());
if(group_id[cycle1[0]] == group_id[cycle2[0]]) {
cout << -1 << endl;
for(int i : tour1) ans.push_back(i);
for(int i : cycle1) ans.push_back(i);
for(int i : tour1r) ans.push_back(i);
for(int i : tour2) ans.push_back(i);
for(int i : cycle2r) ans.push_back(i);
for(int i : tour2r) ans.push_back(i);
//ans.push_back(-2);
//for(int i : cycle1) ans.push_back(i);
//ans.push_back(-3);
//for(int i : cycle2) ans.push_back(i);
} else {
return false;
for(int i : tour1) ans.push_back(i);
for(int i : cycle1) ans.push_back(i);
for(int i : tour1r) ans.push_back(i);
for(int i : tour2) ans.push_back(i);
for(int i : cycle2) ans.push_back(i);
for(int i : tour2r) ans.push_back(i);
for(int i : tour1) ans.push_back(i);
for(int i : cycle1r) ans.push_back(i);
for(int i : tour1r) ans.push_back(i);
for(int i : tour2) ans.push_back(i);
for(int i : cycle2r) ans.push_back(i);
for(int i : tour2r) ans.push_back(i);
//ans.push_back(-1);
}
return true;
}
std::variant<bool, std::vector<int>> find_journey(int _N, int M, std::vector<int> U, std::vector<int> V) {
N = _N;
for(int i = 0; i < N; i++) {
graph[i].clear();
bck[i].clear();
is_cycle[i] = false;
vis[i] = false;
group_id[i] = -1;
}
groups.clear();
for(int i = 0; i < M; i++) {
graph[U[i]].push_back({V[i], i});
bck[V[i]].push_back({U[i], i});
}
topo.clear();
for(int i = 0; i < N; i++) vis[i] = false;
dfs(0);
for(int i = 0; i < N; i++) vis[i] = false;
reverse(topo.begin(), topo.end());
cur_group_id = -1;
for(int i : topo) {
if(vis[i]) continue;
cur_group_id++;
groups.push_back({});
dfs2(i);
}
for(int i = 0; i < N; i++) vis[i] = false;
for(int i = 0; i < groups.size(); i++) {
if(groups[i].size() == 1) continue;
int tmp = groups[i][0];
while(!vis[tmp]) {
vis[tmp] = true;
for(auto [nxt, id] : graph[tmp]) {
if(group_id[nxt] != group_id[tmp]) continue;
cycle_next[tmp] = {nxt, id};
tmp = nxt;
break;
}
}
int tmp2 = tmp;
do {
is_cycle[tmp2] = true;
tmp2 = cycle_next[tmp2].first;
} while(tmp2 != tmp);
}
//for(int i = 0; i < N; i++) {
// cout << cycle_next[i].first << " " << cycle_next[i].second << endl;
//}
for(int bit = (1<<17); bit >= 1; bit >>= 1) {
if(test_cycle(bit)) return ans;
}
return 0;
}