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  • Cow Marathon(树的直径)

    Cow Marathon
    Time Limit: 2000MS   Memory Limit: 30000K
    Total Submissions: 5362   Accepted: 2634
    Case Time Limit: 1000MS

    Description

    After hearing about the epidemic of obesity in the USA, Farmer John wants his cows to get more exercise, so he has committed to create a bovine marathon for his cows to run. The marathon route will include a pair of farms and a path comprised of a sequence of roads between them. Since FJ wants the cows to get as much exercise as possible he wants to find the two farms on his map that are the farthest apart from each other (distance being measured in terms of total length of road on the path between the two farms). Help him determine the distances between this farthest pair of farms. 

    Input

    * Lines 1.....: Same input format as "Navigation Nightmare".

    Output

    * Line 1: An integer giving the distance between the farthest pair of farms. 

    Sample Input

    7 6
    1 6 13 E
    6 3 9 E
    3 5 7 S
    4 1 3 N
    2 4 20 W
    4 7 2 S
    

    Sample Output

    52
    

    Hint

    The longest marathon runs from farm 2 via roads 4, 1, 6 and 3 to farm 5 and is of length 20+3+13+9+7=52. 

    Source

     
    【思路】
    求树的直径。树上最远两点距离。两遍dfs。bfs也可。
    W S E N 并没有什么卵用‘
    【code】
    #include<iostream>
    #include<cstdio>
    #include<cstring>
    using namespace std;
    int n,m,x,y,z,head[40002],dad[40002],dis[40003],maxx,maxn,sumedge;
    struct Edge
    {
        int x,y,z,nxt;
        Edge(int x=0,int y=0,int z=0,int nxt=0):
            x(x),y(y),z(z),nxt(nxt){}
    }edge[80009];
    void add(int x,int y,int z)
    {
        edge[++sumedge]=Edge(x,y,z,head[x]);
        head[x]=sumedge;
    }
    void dfs(int x)
    {
        for(int i=head[x];i;i=edge[i].nxt)
        {
            int v=edge[i].y;
            if(dad[x]!=v)
            {
                dad[v]=x;
                dis[v]=dis[x]+edge[i].z;
                dfs(v);
            }
        }
    }
    int main()
    {
        scanf("%d%d",&n,&m);
        for(int i=1;i<=m;i++)
        {
            char s[4];
            cin>>x>>y>>z>>s[0];
            add(x,y,z);
            add(y,x,z);
        }
        dfs(1);
        maxx=-0x7fffff;
        for(int i=1;i<=n;i++)
        {
            if(dis[i]>maxx)
            {
                maxx=dis[i];
                maxn=i;
            }
        }
        memset(dis,0,sizeof(dis));
        memset(dad,0,sizeof(dad));
        dfs(maxn);
        maxx=-0x7fff;
        for(int i=1;i<=n;i++)
        {
            if(dis[i]>maxx)
            {
                maxx=dis[i];
            }
        }
        printf("%d
    ",maxx);
        return 0;
    } 
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  • 原文地址:https://www.cnblogs.com/zzyh/p/7197298.html
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