BFS

#include <vector>
#include <iostream>
#include <queue>
using namespace std;
const int inf = 2000000000;
vector<vector<int> > g;
vector<int> d;
void bfs(int s)
{
    vector<int> c(d.size());
    c[s] = 1;
    d[s] = 0;
    queue<int> q;
    q.push(s);
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        for(vector<int>::iterator v = g[u].begin(); v != g[u].end(); v++)
            if(d[*v] > d[u] + 1)
            {
                if(c[*v] == 0)
                    q.push(*v);
                c[*v] = 1;
                d[*v] = d[u] + 1;
            }
    }
}
int main()
{
    int n, m, s;
    cin >> n >> m;
    d.resize(n, inf);
    g.resize(n);
    for(int i = 0; i < m; i++)
    {
        int u, v;
        cin >> u >> v;
        u--;v--;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    cin >> s; s--;
    bfs(s);
    for(int i = 0; i < n; i++)
        cout << "d[" << i + 1 << "] = " << d[i] << "\n";
    return 0;
}