From 99ed7a59809e7afa676afb4079f2323b2f2f4595 Mon Sep 17 00:00:00 2001
From: Lam Haoyin <root@eatswap.org>
Date: Wed, 6 Apr 2022 22:49:17 +0800
Subject: [PATCH] add: 220406-CN [cpp]

---
 cpp/2204/220406-CN.cpp  | 76 +++++++++++++++++++++++++++++++++++++++++
 cpp/2204/CMakeLists.txt |  2 +-
 2 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 cpp/2204/220406-CN.cpp

diff --git a/cpp/2204/220406-CN.cpp b/cpp/2204/220406-CN.cpp
new file mode 100644
index 0000000..aae0d0c
--- /dev/null
+++ b/cpp/2204/220406-CN.cpp
@@ -0,0 +1,76 @@
+#include <vector>
+#include <queue>
+#include <cstring>
+
+class Solution {
+public:
+	static std::vector<int> findMinHeightTrees(int n, const std::vector<std::vector<int>>& edges) {
+		if (n == 1)
+			return {0};
+		int degrees[n], ans[n];
+		std::vector<int> G[n];
+		std::memset(degrees, 0, sizeof degrees);
+		std::memset(ans, 0, sizeof ans);
+		for (const auto& e : edges) {
+			G[e[0]].push_back(e[1]);
+			G[e[1]].push_back(e[0]);
+			++degrees[e[0]];
+			++degrees[e[1]];
+		}
+
+		int x, y, distXY;
+		int father[n];
+		{
+			int dist[n];
+			bool vis[n];
+			std::queue<int> q;
+
+			auto doBFS = [&](int startNode) {
+				q.push(startNode);
+				q.push(0);
+				std::memset(vis, 0, sizeof vis);
+				std::memset(father, 0, sizeof father);
+				vis[startNode] = true;
+				while (!q.empty()) {
+					int idx = q.front();
+					q.pop();
+					int len = q.front();
+					q.pop();
+					dist[idx] = len;
+					for (int nextId : G[idx]) {
+						if (vis[nextId])
+							continue;
+						vis[nextId] = true;
+						father[nextId] = idx;
+						q.push(nextId);
+						q.push(len + 1);
+					}
+				}
+			};
+
+			// From 0, find the max distance
+			doBFS(0);
+			x = std::max_element(dist, dist + n) - dist;
+
+			// From x, find the max distance
+			doBFS(x);
+			auto* maxDistPtr = std::max_element(dist, dist + n);
+			y = maxDistPtr - dist;
+			distXY = *maxDistPtr;
+		}
+
+		std::vector<int> ret;
+		int ptr = y;
+		for (int i = 0; i < distXY / 2; ++i)
+			ptr = father[ptr];
+		ret.push_back(ptr);
+		if (distXY & 1)
+			ret.push_back(father[ptr]);
+		return ret;
+	}
+};
+
+int main() {
+	auto ret = Solution::findMinHeightTrees(2, {{0, 1}});
+	return 0;
+}
diff --git a/cpp/2204/CMakeLists.txt b/cpp/2204/CMakeLists.txt
index 94ac5e4..8642583 100644
--- a/cpp/2204/CMakeLists.txt
+++ b/cpp/2204/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2204)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2204 220405.cpp)
+ADD_EXECUTABLE(2204 220406-CN.cpp)