B4016 树的直径

https://www.luogu.com.cn/record/169658881

Luogu/B4016/B4016.cpp

@@ -0,0 +1,49 @@
+#include <iostream>
+#include <algorithm>
+#include <iterator>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e5 + 5;
+
+int n, dep[N];
+std::vector<int> g[N];
+
+void dfs(int u, int fa) {
+    dep[u] = dep[fa] + 1;
+
+    for (int v : g[u]) {
+        if (v == fa) continue;
+
+        dfs(v, u);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1, u, v; i < n; i++) {
+        cin >> u >> v;
+
+        g[u].emplace_back(v);
+        g[v].emplace_back(u);
+    }
+
+    dfs(1, 0);
+
+    int u = std::max_element(dep + 1, dep + n + 1) - dep;
+
+    std::fill(std::begin(dep), std::end(dep), 0);
+
+    dfs(u, 0);
+
+    cout << *std::max_element(dep + 1, dep + n + 1) - 1 << endl;
+
+    return 0;
+}