Computer

A school bought the first computer some time ago(so this computer‘s id is 1). During the recent years the school bought N-1 new computers. Each new computer was connected to one of settled earlier. Managers of school are anxious about slow functioning of the net and want to know the maximum distance Si for which i-th computer needs to send signal (i.e. length of cable to the most distant computer). You need to provide this information. 


Hint: the example input is corresponding to this graph. And from the graph, you can see that the computer 4 is farthest one from 1, so S1 = 3. Computer 4 and 5 are the farthest ones from 2, so S2 = 2. Computer 5 is the farthest one from 3, so S3 = 3. we also get S4 = 4, S5 = 4.

5
1 1
2 1
3 1
1 1

3
2
3
4
4

求树上一点到其它点的最远距离，先以任一点为根节点，进行一次bfs搜到距离当前点最远的点root1，从root1开始再搜，得到root2，从root2再搜一次得到最终答案，每次搜的过程中更新每个点的最远距离。

#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<queue>
#include<vector>
using namespace std;
#define ll long long
#define N 11000
#define mem(a,t) memset(a,t,sizeof(a))
struct node
{
    int v,w,next;
}e[N*2];
int head[N];
int dis[N];
int cnt;
int len_max,root;
void add(int u,int v,int w)
{
    e[cnt].v=v;
    e[cnt].w=w;
    e[cnt].next=head[u];
    head[u]=cnt++;
}

void bfs(int u,int len,int fa)
{
    int i,v;
    if(len>len_max)
    {
        len_max=len;
        root=u;
    }
    for(i=head[u];i!=-1;i=e[i].next)
    {
        v=e[i].v;
        if(v!=fa)
        {
            if(dis[v]<len+e[i].w)
                dis[v]=len+e[i].w;
            bfs(v,len+e[i].w,u);
        }
    }
    return ;
}
int main()
{
    int i,n,a,b;
    while(~scanf("%d",&n))
    {
        mem(head,-1);
        cnt=0;
        for(i=2;i<=n;i++)
        {
            scanf("%d%d",&a,&b);
            add(i,a,b);
            add(a,i,b);
        }
        mem(dis,0);
        len_max=0;
        bfs(1,0,-1);

        len_max=0;
        bfs(root,0,-1);
        bfs(root,0,-1);
        for(i=1;i<=n;i++)
            printf("%d\n",dis[i]);
    }
    return 0;
}

hdu 2196 Computer

原文：http://blog.csdn.net/u011721440/article/details/45369405