130 lines
2.3 KiB
C++
130 lines
2.3 KiB
C++
#include <bits/stdc++.h> // {{{
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#include <version>
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#ifdef __cpp_lib_ranges_enumerate
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#include <ranges>
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namespace rv = std::views;
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namespace rs = std::ranges;
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#endif
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// https://codeforces.com/blog/entry/96344
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#pragma GCC optimize("O2,unroll-loops")
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#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
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using namespace std;
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using i32 = int32_t;
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using u32 = uint32_t;
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using i64 = int64_t;
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using u64 = uint64_t;
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using f64 = double;
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using f128 = long double;
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#if __cplusplus >= 202002L
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template <typename T>
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constexpr T MIN = std::numeric_limits<T>::min();
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template <typename T>
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constexpr T MAX = std::numeric_limits<T>::max();
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template <typename T>
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[[nodiscard]] static T sc(auto&& x) {
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return static_cast<T>(x);
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}
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template <typename T>
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[[nodiscard]] static T sz(auto&& x) {
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return static_cast<T>(x.size());
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}
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#endif
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static void NO() {
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std::cout << "NO\n";
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}
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static void YES() {
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std::cout << "YES\n";
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}
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template <typename T>
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using vec = std::vector<T>;
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#define all(x) (x).begin(), (x).end()
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#define rall(x) (x).rbegin(), (x).rend()
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#define ff first
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#define ss second
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#ifdef LOCAL
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#define db(...) std::print(__VA_ARGS__)
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#define dbln(...) std::println(__VA_ARGS__)
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#else
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#define db(...)
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#define dbln(...)
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#endif
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// }}}
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bitset<2 * 100000 + 1> seen;
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void solve() {
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seen.reset();
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u32 n, m;
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cin >> n >> m;
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vec<vec<u32>> graph(n + 1);
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for (u32 i = 0; i < m; ++i) {
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u32 u, v;
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cin >> u >> v;
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graph[u].push_back(v);
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graph[v].push_back(u);
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}
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auto dfs = [&](auto&& self, u32 u) {
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if (seen[u]) {
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return;
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}
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seen[u] = true;
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for (auto v : graph[u]) {
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self(self, v);
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}
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};
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vec<u32> component_roots;
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for (u32 u = 1; u <= n; ++u) {
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if (!seen[u]) {
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dfs(dfs, u);
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component_roots.push_back(u);
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}
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}
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cout << component_roots.size() - 1 << '\n';
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for (i32 i = 0; i < component_roots.size() - 1; ++i) {
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cout << component_roots[i] << ' ' << component_roots[i + 1] << '\n';
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}
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}
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int main() { // {{{
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std::cin.exceptions(std::cin.failbit);
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#ifdef LOCAL
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std::cerr.rdbuf(std::cout.rdbuf());
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std::cout.setf(std::ios::unitbuf);
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std::cerr.setf(std::ios::unitbuf);
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#else
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std::cin.tie(nullptr)->sync_with_stdio(false);
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#endif
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u32 tc = 1;
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// std::cin >> tc;
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for (u32 t = 0; t < tc; ++t) {
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solve();
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}
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return 0;
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}
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// }}}
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