From af0b89f5c80cfceb8d2fab5b06e4ed42f8a0c2ca Mon Sep 17 00:00:00 2001
From: Baoshuo <i@baoshuo.ren>
Date: Sun, 29 Jan 2023 10:20:11 +0800
Subject: [PATCH] G - Subgraph Isomorphism

https://codeforces.com/gym/104090/submission/191043121
---
 Gym/104090/G/G.cpp | 128 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 128 insertions(+)
 create mode 100644 Gym/104090/G/G.cpp

diff --git a/Gym/104090/G/G.cpp b/Gym/104090/G/G.cpp
new file mode 100644
index 00000000..c742fbbb
--- /dev/null
+++ b/Gym/104090/G/G.cpp
@@ -0,0 +1,128 @@
+#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;
+}