hdu 4679 Terrorist’s destroy (DP or 树直径,4级)
Terrorist’s destroy
Time Limit: 6000/3000 MS (Java/Others) Memory Limit: 65535/32768 K (Java/Others)Total Submission(s): 132 Accepted Submission(s): 20
Problem Description
There is a city which is built like a tree.A terrorist wants to destroy the city's roads. But now he is alone, he can only destroy one road, then the city will be divided into two cities. Impression of the city is a number defined
as the distance between the farthest two houses (As it relates to the fare).When the terrorist destroyed a road, he needs to spend some energy, assuming that the number is a.At the same time,he will get a number b which is maximum of the Impression of two
cities. The terrorist wants to know which road to destroy so that the product of a and b will be minimized.You should find the road's id.
Note that the length of each road is one.
Note that the length of each road is one.
Input
The first line contains integer T(1<=T<=20), denote the number of the test cases.
For each test cases,the first line contains a integer n(1 < n <= 100000);denote the number of the houses;
Each of the following (n-1) lines contains third integers u,v,w, indicating there is a road between house u and houses v,and will cost terrorist w energy to destroy it.The id of these road is number from 1 to n-1.(1<=u<=n , 1<=v<=n , 1<=w<=10000)
For each test cases,the first line contains a integer n(1 < n <= 100000);denote the number of the houses;
Each of the following (n-1) lines contains third integers u,v,w, indicating there is a road between house u and houses v,and will cost terrorist w energy to destroy it.The id of these road is number from 1 to n-1.(1<=u<=n , 1<=v<=n , 1<=w<=10000)
Output
For each test case, output the case number first,and then output the id of the road which the terrorist should destroy.If the answer is not unique,output the smallest id.
Sample Input
2 5 4 5 1 1 5 1 2 1 1 3 5 1 5 1 4 1 1 3 1 5 1 1 2 5 1
Sample Output
Case #1: 2 Case #2: 3
Source
Recommend
zhuyuanchen520
思路:找树直径,删边不在直径上,最长即是直径,在直径上,算切往直径剩下的最大长度。
#pragma comment(linker, "/STACK:1024000000,1024000000") #include<iostream> #include<cstring> #include<cstdio> #define FOR(i,a,b) for(int i=a;i<=b;++i) #define clr(f,z) memset(f,z,sizeof(f)) #define LL __int64 using namespace std; const int mm=2e5+9; int head[mm],edge,n,dis[mm]; class Edge { public:int v,next,val,id; bool yes; }e[mm]; int ans,len; LL cun; void data() { clr(head,-1);edge=0; } void add(int u,int v,int c,int id) { e[edge].id=id;e[edge].yes=0; e[edge].v=v;e[edge].val=c;e[edge].next=head[u];head[u]=edge++; } void dfs(int u,int fa) { int v; for(int i=head[u];~i;i=e[i].next) { v=e[i].v; if(v==fa)continue; if(dis[v]>dis[u]+1) {dis[v]=dis[u]+1; dfs(v,u); } } } void dfs1(int u,int fa) { int v; for(int i=head[u];~i;i=e[i].next) { v=e[i].v; if(v==fa)continue; if(dis[v]+1==dis[u]) { e[i].yes=1;e[i^1].yes=1; dfs1(v,u); } } } void dfs2(int u,int fa) { int v,lu,lv; for(int i=head[u];~i;i=e[i].next) { v=e[i].v; if(v==fa)continue; dfs2(v,u); if(dis[u]>dis[v]) { lv=dis[v];lu=len-dis[u]; } else { lv=len-dis[v];lu=dis[u]; } LL kz=max(lv,lu); //printf("ld=%d %d %d\n",u,v,kz); if(!e[i].yes)kz=len; LL kv=e[i].val; LL z=kv*kz; if(ans==0) { ans=e[i].id;cun=z; } else if(z<cun) { ans=e[i].id;cun=z; } else if(z==cun&&e[i].id<ans) { ans=e[i].id; } } } void solve() { clr(dis,0x3f); dis[1]=0; dfs(1,-1); int kai=1; FOR(i,1,n)///找树直径 if(dis[kai]<dis[i])kai=i; clr(dis,0x3f); dis[kai]=0; dfs(kai,-1);//get longest kai=1; FOR(i,1,n) if(dis[kai]<dis[i])kai=i; len=dis[kai]; //cout<<" len="<<len<<endl; dfs1(kai,-1);///标记最长 ans=0; dfs2(kai,-1); printf("%d\n",ans); } int main() { int cas,a,b,c; while(~scanf("%d",&cas)) { FOR(ca,1,cas) { data(); scanf("%d",&n); FOR(i,1,n-1) { scanf("%d%d%d",&a,&b,&c); add(a,b,c,i);add(b,a,c,i); } printf("Case #%d: ",ca); solve(); } } return 0; }
The article write by nealgavin