[HihoCoder]#1050 : 树中的最长路

// problem1050.cpp : 定义控制台应用程序的入口点。
// #1050 : 树中的最长路
// 张正义 2016-05-15

#include "stdafx.h"

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

int BroadVisit(vector<vector<int>> &edgeList, int start, int &end)
{
int depth = -1;
queue<int> q;
vector<bool> visited(edgeList.size());
q.push(-1);
q.push(start);
while (q.empty()==false)
{
if (q.front() == -1)
{
q.pop();
q.push(-1);
if (q.front() == -1)
{
break;
}
depth++;
}
int nodeNum = q.front();
q.pop();
visited[nodeNum] = true;
for (int i = 0; i < edgeList[nodeNum].size(); i++)
{
if (visited[edgeList[nodeNum][i]] == false)
{
end = edgeList[nodeNum][i];
q.push(end);
}
}
}
return depth;
}

int main()
{
int n;
cin >> n;
vector<vector<int>> edgeList(n);
for (int i = 0; i < n - 1; i++)
{
int p1, p2;
cin >> p1 >> p2;
p1--; p2--;
edgeList[p1].push_back(p2);
edgeList[p2].push_back(p1);
}
int end;
BroadVisit(edgeList, 0, end);
cout << BroadVisit(edgeList, end, end) << endl;
return 0;
}