1072. 树的最长路径

https://www.acwing.com/problem/content/submission/code_detail/13222443/

AcWing/1072/1072.cpp

@@ -0,0 +1,52 @@
+#include <iostream>
+#include <vector>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 10005;
+
+int n, ans;
+std::vector<std::pair<int, int>> g[N];
+
+int dfs(int u, int fa) {
+    int d1 = 0, d2 = 0;
+
+    for (auto e : g[u]) {
+        int v = e.first,
+            w = e.second;
+
+        if (v == fa) continue;
+
+        int d = dfs(v, u) + w;
+        if (d >= d1) {
+            d2 = d1;
+            d1 = d;
+        } else if (d > d2) {
+            d2 = d;
+        }
+    }
+
+    ans = std::max(ans, d1 + d2);
+
+    return d1;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+    for (int i = 1, u, v, w; i < n; i++) {
+        cin >> u >> v >> w;
+
+        g[u].push_back(std::make_pair(v, w));
+        g[v].push_back(std::make_pair(u, w));
+    }
+
+    dfs(1, -1);
+
+    cout << ans << endl;
+
+    return 0;
+}