SPOJ-PT07Z.cpp

#include <cstdio>
#include <iostream>
#include <vector>
#define N 101
using namespace std;

int max(int a,int b){
  if(a>b) 
		return a;
	else 
		return b;
}

int Visited[100000+1]={0};
int min0[100000+1]={0};
int min1[100000+1]={0};
vector<int> *AL;

int fn(int v)
{
	int i,j,r0,r1;
	vector <int> & k = AL[v];
	r0=0;
	Visited[v] = 1; 
//	printf("%d\n", v);
	for(i=0;i<k.size();i++)
	{
			j = k[i];
			if(Visited[j]==0)
			{ 
				fn(j);		
				r0=max(min1[j],min0[j])+1;
				if(min0[v]<r0)
				{
					min1[v]=min0[v];
					min0[v]=r0;
				}
				else if(min1[v]<r0)
					min1[v]=r0;
			}
	}
}

int main()
{
	int n,a,b;
	scanf("%d", &n);
	AL = new vector<int>[n+1];
	for(int i=0;i<n-1;i++){
		scanf("%d%d", &a,&b);
		AL[a].push_back(b);
		AL[b].push_back(a);
	}	
	fn(1);
	a=0;
	for(int i=1;i<=n;i++){
//		printf("%d %d %d\n",i, min1[i],min0[i] );
		if(a<(min1[i]+min0[i])) 
			a = (min1[i]+min0[i]);
	}
	
	printf("%d\n", a );
	delete []AL;
	return 0;
}