Shortest path using BFS

#include <bits/stdc++.h>
#define mx (int) 10000
#define mem(a, b) memset(a, b, sizeof(a))
using namespace std;

vector<int> adj[mx];
int level[mx];
vector<int> parent(mx, -1);

void bfs(int s) {
    level[s] = 0;
    queue<int> q;
    q.push(s);
    while (!q.empty()) {
        int u = q.front();
        q.pop();
        for (auto v : adj[u]) {
            if (level[v] == -1) {
                level[v] = level[u] + 1;
                q.push(v);
                parent[v] = u;
            }
        }
    }
}

int main() {
    mem(level, -1);

    int n, e;
    cin >> n >> e;
    for (int i = 0; i < e; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    int source, dest;
    cin >> source >> dest;

    bfs(source);

    if (level[dest] == 0) {
        cout << "No route\n";
        return 0;
    }

    vector<int> ans;
    ans.push_back(dest);
    while (parent[dest] != -1) {
        ans.push_back(parent[dest]);
        dest = parent[dest];
    }

    reverse(ans.begin(), ans.end());

    for (auto u : ans) {
        cout << u << " ";
    }
    cout << endl;
}