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HDU 4460 Friend Chains --BFS

题意:问给定的一张图中,相距最远的两个点的距离为多少。
解法:跟求树的直径差不多,从1 开始bfs,得到一个最远的点,然后再从该点bfs一遍,得到的最长距离即为答案。

代码:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <map>
using namespace std;
#define N 100007

map<string,int> mp;
vector<int> G[1006];
int vis[1006],n,m,Maxdis,Maxtag;
struct node{
    int dis,u;
};

void dfs(int u)
{
    vis[u] = 1;
    for(int i=0;i<G[u].size();i++)
    {
        int v = G[u][i];
        if(!vis[v]) dfs(v);
    }
}

void bfs(int u)
{
    queue<node> que;
    memset(vis,0,sizeof(vis));
    node now;
    now.dis = 0;
    now.u = u;
    que.push(now);
    vis[u] = 1;
    while(!que.empty())
    {
        int SZ = que.size();
        while(SZ--)
        {
            node tmp = que.front();
            que.pop();
            int dis = tmp.dis;
            int u = tmp.u;
            if(dis > Maxdis)
            {
                Maxdis = dis;
                Maxtag = u;
            }
            for(int i=0;i<G[u].size();i++)
            {
                int v = G[u][i];
                if(!vis[v])
                {
                    now.u = v;
                    now.dis = dis+1;
                    vis[v] = 1;
                    que.push(now);
                }
            }
        }
    }
}

int main()
{
    int i,j;
    string S;
    while(scanf("%d",&n)!=EOF && n)
    {
        mp.clear();
        for(i=1;i<=n;i++)
        {
            cin>>S;
            mp[S] = i;
            G[i].clear();
        }
        scanf("%d",&m);
        string A,B;
        for(i=1;i<=m;i++)
        {
            cin>>A>>B;
            int a = mp[A], b = mp[B];
            G[a].push_back(b);
            G[b].push_back(a);
        }
        memset(vis,0,sizeof(vis));
        dfs(1);
        int Link = 1;
        for(i=1;i<=n;i++)
            if(!vis[i]) Link = 0;
        if(!Link)
        {
            puts("-1");
            continue;
        }
        Maxdis = 0, Maxtag = -1;
        bfs(1);
        int S = Maxtag;
        Maxdis = 0, Maxtag = -1;
        bfs(S);
        printf("%d\n",Maxdis);
    }
    return 0;
}
View Code

 

posted @ 2014-11-08 21:39  whatbeg  阅读(207)  评论(0编辑  收藏  举报