首页 > 代码库 > POJ 1985 Cow Marathon(树的直径)
POJ 1985 Cow Marathon(树的直径)
Cow Marathon
Time Limit: 2000MS | Memory Limit: 30000K | |
Total Submissions: 5357 | Accepted: 2630 | |
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 61 6 13 E6 3 9 E3 5 7 S4 1 3 N2 4 20 W4 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
USACO 2004 February
先假设节点1是根节点,
跑到离他最远的点,
再从最远的点开始跑,
跑到的最远的的点就是树的直径
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cmath> 5 #define lli long long int 6 using namespace std; 7 const int MAXN=100001; 8 void read(int &n) 9 {10 char c=‘+‘;int x=0;bool flag=0;11 while(c<‘0‘||c>‘9‘){c=getchar();if(c==‘-‘)flag=1;}12 while(c>=‘0‘&&c<=‘9‘)13 x=(x<<1)+(x<<3)+c-48,c=getchar();14 flag==1?n=-x:n=x;15 }16 struct node17 {18 int u,v,w,nxt;19 }edge[MAXN];20 int head[MAXN];21 int num=1;22 int n,m;23 void add_edge(int x,int y,int z)24 {25 edge[num].u=x;26 edge[num].v=y;27 edge[num].w=z;28 edge[num].nxt=head[x];29 head[x]=num++;30 }31 int dp[MAXN];32 int ans=0;33 int ed=0;34 void dfs(int u,int fa,int now)35 {36 if(now>ans)37 {38 ans=now;39 ed=u;40 }41 for(int i=head[u];i!=-1;i=edge[i].nxt)42 {43 if(edge[i].v!=fa)44 dfs(edge[i].v,u,now+edge[i].w);45 }46 }47 int main()48 {49 read(n);read(m);50 memset(head,-1,sizeof(head));51 for(int i=1;i<=m;i++)52 {53 int x,y,z;char c;54 read(x);read(y);read(z);55 cin>>c;56 add_edge(x,y,z);57 add_edge(y,x,z);58 }59 dfs(1,0,0);60 dfs(ed,0,0);61 printf("%d",ans);62 return 0;63 }
POJ 1985 Cow Marathon(树的直径)
声明:以上内容来自用户投稿及互联网公开渠道收集整理发布,本网站不拥有所有权,未作人工编辑处理,也不承担相关法律责任,若内容有误或涉及侵权可进行投诉: 投诉/举报 工作人员会在5个工作日内联系你,一经查实,本站将立刻删除涉嫌侵权内容。