POJ 2349 Arctic Network(最小生成树之Prim)
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Arctic Network
Time Limit: 2000MS Memory Limit: 65536KTotal Submissions: 0 Accepted: 0
Description
The Department of National Defence (DND) wishes to connect several northern outposts by a wireless network. Two different communication technologies are to be used in establishing the network: every outpost will have a radio transceiver and some outposts will in addition have a satellite channel.
Any two outposts with a satellite channel can communicate via the satellite, regardless of their location. Otherwise, two outposts can communicate by radio only if the distance between them does not exceed D, which depends of the power of the transceivers. Higher power yields higher D but costs more. Due to purchasing and maintenance considerations, the transceivers at the outposts must be identical; that is, the value of D is the same for every pair of outposts.
Your job is to determine the minimum D required for the transceivers. There must be at least one communication path (direct or indirect) between every pair of outposts.
Any two outposts with a satellite channel can communicate via the satellite, regardless of their location. Otherwise, two outposts can communicate by radio only if the distance between them does not exceed D, which depends of the power of the transceivers. Higher power yields higher D but costs more. Due to purchasing and maintenance considerations, the transceivers at the outposts must be identical; that is, the value of D is the same for every pair of outposts.
Your job is to determine the minimum D required for the transceivers. There must be at least one communication path (direct or indirect) between every pair of outposts.
Input
The first line of input contains N, the number of test cases. The first line of each test case contains 1 <= S <= 100, the number of satellite channels, and S < P <= 500, the number of outposts. P lines follow, giving the (x,y) coordinates of each outpost in km (coordinates are integers between 0 and 10,000).
Output
For each case, output should consist of a single line giving the minimum D required to connect the network. Output should be specified to 2 decimal points.
Sample Input
12 40 1000 3000 600150 750
Sample Output
212.13
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附上该题对应的中文题
题意:有两种不同的通信技术,有卫星通信的两个城市之间可以任意联络,但用无线电通信的城市只能和距离不超过D的城市联系。无线电的能力越高(即传输距离D越大),花费就越大。已知无线电的数目m,求最小的D。思路:先求出每两个顶点之间的距离,(注意:是double类型的),然后用普里姆算法(Prim)求最小生成树。由于无线电的数目已给出m,所以需要把最小生成树分成m份,即删除m-1条边,得到m个连通分量。关键是删除哪些边呢,题目要求最小的D,故把构成最小生成树的边从大到小排序,删除前m-1条边,第m条边即所要求的最小D。其实只要思路清晰,很容易就能把这道题AC。
#pragma comment(linker, "/STACK:1024000000,1024000000")#include<stdio.h>#include<string.h>#include<stdlib.h>#include<queue>#include<stack>#include<math.h>#include<vector>#include<map>#include<set>#include<stdlib.h>#include<cmath>#include<string>#include<algorithm>#include<iostream>#define exp 1e-10using namespace std;const int N = 501;const double inf = 1000000000;const int mod = 2009;double x[N],y[N],s[N][N],ans[N],d[N];bool v[N];int p,q;void prim(int x){ int i,j,k; double Min; v[x]=true; for(j=1;j<=p;j++) if(j!=x) d[j]=s[x][j]; for(i=1;i<p;i++) { Min=inf; for(j=1;j<=p;j++) if(Min>d[j]&&!v[j]) Min=d[k=j]; ans[q++]=Min; v[k]=true; for(j=1;j<=p;j++) if(d[j]>s[k][j]) d[j]=s[k][j]; }}int main(){ int t,n,i,j; scanf("%d",&t); while(t--) { memset(v,false,sizeof(v)); q=0; scanf("%d%d",&n,&p); for(i=1;i<=p;i++) scanf("%lf%lf",&x[i],&y[i]); for(i=1;i<=p;i++) for(j=1;j<=i;j++) if(i==j) s[i][j]=inf; else s[i][j]=s[j][i]=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j])); prim(1); sort(ans,ans+q); printf("%.2f\n",ans[q-n]); } return 0;}菜鸟成长记
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