BFS

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>

using namespace std;

#define si(a) scanf("%d",&a)
#define f first
#define s second
#define mp(a,b) make_pair(a,b)
#define MAX 1005

int dist[MAX];
vector<int> graph[MAX];

void bfs(int st)
{
    queue<pair<int,int> > Q;
    Q.push(mp(st,0));
    memset(dist,-1,sizeof(dist));
    while(!Q.empty()){
        pair<int,int> now=Q.front();
        Q.pop();
        if(dist[now.f]!=-1)
            continue;
        dist[now.f]=now.s;
        //cout<<now.f+1<<" "<<now.s<<endl;
        for(int i=0;i<graph[now.f].size();i++)
            Q.push(mp(graph[now.f][i],now.s+1));
    }
    return ;
}

int main()
{
    //freopen("input","r",stdin);
    int n,m,i;
    si(n);si(m);
    for(i=0;i<m;i++){
        int u,v;
        si(u);si(v);
        u--;v--;
        graph[u].push_back(v);
        graph[v].push_back(u);
    }
    bfs(0);
    return 0;
}