Another problem from a placement test, based on modified BFS, done for a friend.

festiveCities.cpp

#include <iostream>
#include <vector>
#include <queue>

#define INF 1000000007
using namespace std;
typedef vector<vector<int> > graph;

void updateDist(graph &g, vector<int> &dist, int src){
    queue<int> q;
    vector<bool> visited(g.size(), false);
    int v;
    q.push(src);
    dist[src] = 0;

    while(! q.empty()){
        v = q.front();
        q.pop();
        for(int i=0; i<g[v].size(); ++i){
            if(!visited[g[v][i]]){
                if(dist[g[v][i]] > dist[v]+1){
                    dist[g[v][i]] = dist[v]+1;
                    q.push(g[v][i]);
                }
            }
        }
    }
}

int main(){
    int n, m, u, v;
    cin >> n >> m;
    vector<int> dist(n+1, INF);
    graph g(n+1, vector<int>());
    
    for(int a=0; a<n-1; a++){
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    updateDist(g, dist, 1);
    for(int a=0; a<m; a++){
        cin >> u >> v;
        if(u==1) updateDist(g, dist, v);
        else cout << dist[v] << endl;
    }
    return 0;
}