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OI-codes/Gym/103081/I/I.cpp

57 lines
1.0 KiB
C++

#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;
}