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OI-codes/S2OJ/1850/1850.cpp

129 lines
2.6 KiB
C++

#include <iostream>
#include <functional>
#include <stack>
#include <unordered_set>
#include <vector>
using std::cin;
using std::cout;
const char endl = '\n';
// 树哈希
// https://peehs-moorhsum.blog.uoj.ac/blog/7891
unsigned long long h(unsigned long long x) {
return x * x * x * 1237123 + 19260817;
}
unsigned long long f(unsigned long long x) {
return h(x & ((1ull << 31) - 1)) + h(x >> 31);
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
int t;
cin >> t;
while (t--) {
int n, m;
cin >> n >> m;
std::vector<std::vector<int>> g(n + 1);
for (int i = 1, x, y; i <= m; i++) {
cin >> x >> y;
g[x].emplace_back(y);
g[y].emplace_back(x);
}
if (m > n) {
cout << "NO" << endl;
continue;
}
if (m < n) {
cout << "YES" << endl;
continue;
}
// assert(n == m);
std::stack<int> st;
std::vector<int> circle;
std::vector<bool> vis1(n + 1);
std::function<void(int, int)> dfs1 = [&](int u, int f) -> void {
if (vis1[u]) {
if (circle.empty()) {
while (!st.empty() && st.top() != u) {
circle.emplace_back(st.top());
st.pop();
}
circle.emplace_back(u);
}
return;
}
vis1[u] = true;
st.emplace(u);
for (int v : g[u]) {
if (v == f) continue;
dfs1(v, u);
}
if (!st.empty()) st.pop();
};
dfs1(1, 0);
std::vector<bool> vis2(n + 1);
std::vector<unsigned long long> hash(n + 1);
std::unordered_set<unsigned long long> set;
for (int x : circle) vis2[x] = true;
std::function<void(int)> dfs2 = [&](int u) -> void {
vis2[u] = true;
hash[u] = 1;
for (int v : g[u]) {
if (vis2[v]) continue;
dfs2(v);
hash[u] += f(hash[v]);
}
};
for (int x : circle) {
dfs2(x);
set.emplace(hash[x]);
}
bool flag = circle.size() % 2 == 0;
for (int i = 0; i + 2 < circle.size(); i++) {
if (hash[circle[i]] != hash[circle[i + 2]]) {
flag = false;
break;
}
}
cout << (set.size() == 1 || flag ? "YES" : "NO") << endl;
}
return 0;
}