From c9a12839fcdec08f4c43b25c23caa9bf965053e8 Mon Sep 17 00:00:00 2001
From: Amit Kumar <112179674+yogmanamit@users.noreply.github.com>
Date: Mon, 23 Oct 2023 22:54:18 +0530
Subject: [PATCH] Add files via upload

---
 GoodColorings-1887E/ans.cpp | 92 +++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 GoodColorings-1887E/ans.cpp

diff --git a/GoodColorings-1887E/ans.cpp b/GoodColorings-1887E/ans.cpp
new file mode 100644
index 0000000..d2d96f1
--- /dev/null
+++ b/GoodColorings-1887E/ans.cpp
@@ -0,0 +1,92 @@
+// https://codeforces.com/contest/1887/problem/E
+#include <bits/stdc++.h>
+
+using i64 = long long;
+
+void solve() {
+    int n;
+    std::cin >> n;
+    
+    std::vector<std::vector<std::pair<int, int>>> adj(2 * n);
+    for (int i = 0; i < 2 * n; i++) {
+        int x, y;
+        std::cin >> x >> y;
+        x--, y--;
+        y += n;
+        adj[x].emplace_back(y, i);
+        adj[y].emplace_back(x, i);
+    }
+    
+    std::vector<bool> vis(2 * n);
+    std::vector<int> par(2 * n), dep(2 * n), parc(2 * n);
+    std::vector<int> cyc;
+    std::vector<int> col;
+    auto dfs = [&](auto self, int x) -> void {
+        vis[x] = true;
+        for (auto [y, c] : adj[x]) {
+            if (!vis[y]) {
+                par[y] = x;
+                parc[y] = c;
+                dep[y] = dep[x] + 1;
+                self(self, y);
+            } else if (dep[y] > dep[x] && cyc.empty()) {
+                for (int i = y; i != x; i = par[i]) {
+                    cyc.push_back(i);
+                    col.push_back(parc[i]);
+                }
+                cyc.push_back(x);
+                col.push_back(c);
+            }
+        }
+    };
+    for (int i = 0; i < 2 * n; i++) {
+        if (!vis[i] && cyc.empty()) {
+            dfs(dfs, i);
+        }
+    }
+    
+    assert(!cyc.empty());
+    
+    if (cyc[0] >= n) {
+        std::rotate(cyc.begin(), cyc.begin() + 1, cyc.end());
+        std::rotate(col.begin(), col.begin() + 1, col.end());
+    }
+    
+    while (cyc.size() > 4) {
+        int m = (cyc.size() + 3) / 4 * 2;
+        std::cout << "? " << cyc[0] + 1 << " " << cyc[m - 1] - n + 1 << std::endl;
+        
+        int res;
+        std::cin >> res;
+        res--;
+        
+        if (std::find(col.begin(), col.begin() + m - 1, res) == col.begin() + m - 1) {
+            cyc.erase(cyc.begin() + m, cyc.end());
+            col.erase(col.begin() + m, col.end());
+            col.back() = res;
+        } else {
+            cyc.erase(cyc.begin() + 1, cyc.begin() + m - 1);
+            col.erase(col.begin() + 1, col.begin() + m - 1);
+            col[0] = res;
+        }
+    }
+    
+    std::cout << "! " << cyc[0] + 1 << " " << cyc[2] + 1 << " " << cyc[1] - n + 1 << " " << cyc[3] - n + 1 << std::endl;
+    
+    std::string s;
+    std::cin >> s;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+    
+    int t;
+    std::cin >> t;
+    
+    while (t--) {
+        solve();
+    }
+    
+    return 0;
+}