I - Emails

https://codeforces.com/gym/103081/submission/143726423

Gym/103081/I/I.cpp

@@ -0,0 +1,56 @@
+#include <cmath>
+#include <cstring>
+#include <iostream>
+#include <queue>
+#include <vector>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+const int N = 100005;
+
+int n, m;
+std::vector<int> g[N];
+
+// Shortest Path
+int dist[N], max;
+bool vis[N];
+void spfa() {
+    memset(dist, 0x3f, sizeof(dist));
+    std::queue<int> q;
+    q.push(1);
+    dist[1] = 0;
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+        if (vis[u]) continue;
+        vis[u] = true;
+        for (int v : g[u]) {
+            if (dist[v] > dist[u] + 1) {
+                dist[v] = dist[u] + 1;
+                q.push(v);
+                max = std::max(max, dist[v]);
+            }
+        }
+    }
+}
+
+int main() {
+    cin >> n >> m;
+    for (int i = 1; i <= m; i++) {
+        int u, v;
+        cin >> u >> v;
+        g[u].push_back(v);
+        g[v].push_back(u);
+    }
+    spfa();
+    for (int i = 1; i <= n; i++) {
+        if (dist[i] == 0x3f3f3f3f) {
+            cout << -1 << endl;
+            exit(0);
+        }
+    }
+    cout << (int)ceil(log2(max)) + 1 << endl;
+    return 0;
+}