Spoj_LongestPathInATree

// Spoj: PT07Z - Longest path in a tree
// https://www.spoj.com/problems/PT07Z/

#include<bits/stdc++.h>
#define MAX 10001
#define INF INT_MAX
using namespace std;

void bfs(int source, vector<int> graph[], int dist[], int N){
    for(int i=0; i<=N; i++) dist[i] = -1;
    dist[source] = 0;
    queue<int> q;
    q.push(source);
    while ( !q.empty() ){
        int cur = q.front();
        q.pop();
        for(int i=0; i<graph[cur].size(); i++){
            int next = graph[cur][i];
            if( dist[next] == -1 ){
                q.push(next);
                dist[next] = dist[cur] + 1;
            }
        }
    }
}

int main()
{
    vector<int> graph[MAX];
    int N, u, v;
    int dist[MAX];
    scanf("%d", &N);
    for(int i=0; i<N-1; i++){
        scanf("%d %d", &u, &v);
        graph[u].push_back(v);
        graph[v].push_back(u);
    }
    bfs(1, graph, dist, N);
    int maxDist = -1;
    int indx;
    for(int i=1; i<=N; i++){
        if(dist[i] > maxDist){
            maxDist = dist[i];
            indx = i;
        }
    }
    bfs(indx, graph, dist, N);
    maxDist = -1;
    for(int i=1; i<=N; i++){
        if(dist[i] > maxDist)
            maxDist = dist[i];
    }
    printf("%d\n", maxDist);

    return 0;
}