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publib_bfs_with_array_queue.cc
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publib_bfs_with_array_queue.cc
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#include <cstdio>
#include <queue>
#include <vector>
int main() {
FILE *fi = fopen("publib.in", "r");
long N, M;
fscanf(fi, "%ld%ld", &N, &M);
std::vector<std::vector<long>> adj(N);
while(M--) {
long a, b;
fscanf(fi, "%ld%ld", &a, &b);
a--; b--;
adj[a].push_back(b);
adj[b].push_back(a);
}
fclose(fi);
std::vector<bool> visited(N); // Αν έχουμε επισκεφτεί έναν κόμβο.
std::vector<std::pair<long, long>> q(N); // Η ουρά.
long graph_radius = N + 1;
for (int i = 0; i < N; ++i) {
std::fill(visited.begin(), visited.end(), false);
q[0] = { i, 0 };
visited[i] = true;
long max_dist = 0;
long l = 0, r = 0; // Η ουρά είναι στις θέσεις q[l..r].
// Τρέχουμε την BFS.
while (l <= r) {
auto [v, d] = q[l]; // front
++l; // pop
for (auto neigh : adj[v]) {
if (!visited[neigh]) {
++r;
q[r] = {neigh, d + 1}; // push
visited[neigh] = true;
}
}
max_dist = d;
}
graph_radius = std::min(max_dist, graph_radius);
}
FILE *fo = fopen("publib.out", "w");
fprintf(fo, "%ld\n", graph_radius);
fclose(fo);
return 0;
}