added soln for tree diameter

9_tree_algorithms/tree_diameter.cpp

@@ -0,0 +1,63 @@
+#include <iostream>
+#include <vector>
+#include <queue>
+#include <cstring>
+
+using namespace std;
+
+int n;
+vector<vector<int>> adj;
+
+pair<int, int> bfs(int start_node) {
+    vector<int> dist(n + 1, -1);
+    queue<int> q;
+
+    q.push(start_node);
+    dist[start_node] = 0;
+
+    int farthest_node = start_node;
+    int max_dist = 0;
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+
+        if (dist[u] > max_dist) {
+            max_dist = dist[u];
+            farthest_node = u;
+        }
+
+        for (int v : adj[u]) {
+            if (dist[v] == -1) {
+                dist[v] = dist[u] + 1;
+                q.push(v);
+            }
+        }
+    }
+    return {farthest_node, max_dist};
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+
+    cin >> n;
+    adj.resize(n + 1);
+
+    for (int i = 0; i < n - 1; ++i) {
+        int a, b;
+        cin >> a >> b;
+        adj[a].push_back(b);
+        adj[b].push_back(a);
+    }
+
+    pair<int, int> first_bfs_result = bfs(1);
+    int farthest_node_from_1 = first_bfs_result.first;
+
+    pair<int, int> second_bfs_result = bfs(farthest_node_from_1);
+    int diameter = second_bfs_result.second;
+
+    cout << diameter << "\n";
+
+    return 0;
+}