// --- algolib/union-find.h ---
// union find, optionally with tags for each component. this is useful
// for example when compressing components. enable using template parameter
#include <algorithm>
#include <type_traits>
#include <numeric>
#include <vector>
template<typename T = void, typename enable = void>
class UnionFind {
std::vector<int> p, size_;
public:
UnionFind(int n = 0) : p(n), size_(n, 1) {
std::iota(p.begin(), p.end(), 0);
}
int create() {
int r = p.size();
p.push_back(r);
size_.push_back(1);
return r;
}
int find(int i) {
if (i == p[i])
return i;
return p[i] = find(p[i]);
}
int operator[](int i) { return find(i); }
int size(int i) { return size_[find(i)]; }
bool connected(int a, int b) { return find(a) == find(b); }
bool connect(int a, int b) {
a = find(a), b = find(b);
if (a == b)
return false;
if (size_[a] > size_[b])
std::swap(a, b);
size_[b] += size_[a];
p[a] = b;
return true;
}
};
// connect(a, b) maintains tag(b)
template<typename T>
class UnionFind<T, typename std::enable_if_t<!std::is_same_v<T, void>>>
: public UnionFind<void> {
std::vector<T> tags;
public:
UnionFind(int n = 0) : UnionFind<void>(n), tags(n) { }
void create() {
UnionFind<void>::create();
tags.emplace_back();
}
bool connect(int a, int b) {
T old = tag(b);
bool res = UnionFind<void>::connect(a, b);
set_tag(b, old);
return res;
}
void set_tag(int i, const T& t) { tags[find(i)] = t; }
const T& tag(int i) { return tags[find(i)]; }
};
// ----------------
#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 300005;
int n;
vector<int> ans;
struct Edge {
int to, key; // key required
bool operator<(const Edge& o) const {
// cannot just use key, otherwise edges get lost (set)
return tie(key, to) < tie(o.key, o.to);
}
};
vector<int> out_can[MAX_N]; // only the to
set<Edge> out_blocked[MAX_N];
set<int> keys[MAX_N];
int par[MAX_N]; // parent in tree
UnionFind weakly(MAX_N); // weakly connected components
UnionFind<int> compressed(MAX_N);
// merge i into j, smaller to larger style
void merge(int i, int j) {
if (compressed.size(i) > compressed.size(j)) {
out_can[i].swap(out_can[j]);
out_blocked[i].swap(out_blocked[j]);
keys[i].swap(keys[j]);
}
compressed.connect(i, j); // tag of j is maintained
out_can[j].insert(out_can[j].end(),
out_can[i].begin(), out_can[i].end());
out_can[i].clear();
for (int key : keys[i])
if (keys[j].insert(key).second) { // promote
auto it = out_blocked[j].lower_bound({ -1, key });
while (it != out_blocked[j].end() && it->key == key) {
out_can[j].push_back(it->to);
it = out_blocked[j].erase(it);
}
}
keys[i].clear();
for (auto& x : out_blocked[i])
if (keys[j].find(x.key) == keys[j].end())
out_blocked[j].insert(x);
else if (!compressed.connected(j, x.to)) // pruning back edges
out_can[j].push_back(x.to);
out_blocked[i].clear();
return;
}
void solve() {
using pq_key = pair<int, int>; // size, vertex (roots order by size)
priority_queue<pq_key, vector<pq_key>, greater<pq_key>> roots;
// tags are the representatives (where keys & edges are stored)
for (int i = 0; i < n; i++) {
compressed.set_tag(i, i);
roots.push({ 1, i });
}
// != -1 means we already found an answer of size done_size
// so stop pushing to pq, but collect remaining components
int done_size = -1;
ans.assign(n, 0);
while (!roots.empty()) {
auto [_, r] = roots.top();
roots.pop();
// find any outgoing edge
bool has_outgoing = false;
while (!out_can[r].empty()) {
int to = out_can[r].back();
out_can[r].pop_back();
if (compressed.connected(r, to))
continue;
has_outgoing = true;
if (done_size != -1) // we're larger than the answer
break;
if (weakly.connected(r, to)) {
// merge with self. walk up parents
int j = compressed.tag(to);
do {
int jp = compressed.tag(par[j]);
merge(j, jp);
j = jp;
} while (j != r);
// we're still a root, but of larger size
roots.push({ compressed.size(r), r });
} else { // merge with other component
par[r] = to;
weakly.connect(r, to);
// we're no root any longer (no pq push)
}
break;
}
if (!has_outgoing) {
int size = compressed.size(r);
if (done_size != -1 && size != done_size)
break;
done_size = size;
ans[r] = 1;
}
}
for (int i = 0; i < n; i++) // everthing in their components too
if (ans[compressed.tag(i)])
ans[i] = 1;
}
vector<int> find_reachable(vector<int> r, vector<int> u,
vector<int> v, vector<int> c) {
n = r.size();
for (int i = 0; i < n; i++)
keys[i].insert(r[i]);
for (size_t i = 0; i < u.size(); i++)
for (int x = 0; x < 2; x++) {
if (r[u[i]] == c[i])
out_can[u[i]].push_back(v[i]);
else
out_blocked[u[i]].insert({ v[i], c[i] });
swap(u[i], v[i]);
}
solve();
return ans;
}
Compilation message
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/10/../../../x86_64-linux-gnu/crt1.o: in function `_start':
(.text+0x24): undefined reference to `main'
collect2: error: ld returned 1 exit status
