POJ3771+Prim

最小生成树的应用

数据量小。

/*
Prim
*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
#include<iostream>
#include<queue>
#include<map>
#include<stack>
#include<set>
#include<math.h>
using namespace std;
typedef long long int64;
//typedef __int64 int64;
typedef pair<int64,int64> PII;
#define MP(a,b) make_pair((a),(b)) 
const int maxn = 55;
const double inf = 99999999;
const double pi=acos(-1.0);
const double eps = 1e-8;

struct Node{
	double x,y;
}pnt[ maxn ];
double dis[ maxn ];
bool vis[ maxn ];
double mat[ maxn ][ maxn ];
double dist( int a,int b ){
	return sqrt( (pnt[a].x-pnt[b].x)*(pnt[a].x-pnt[b].x)+(pnt[a].y-pnt[b].y)*(pnt[a].y-pnt[b].y) );
}

double Prim( int start,int aim,int n ){
	double ans = 0;
	memset( vis,false,sizeof( vis ) );
	vis[ start ] = true;
	vis[ aim ] = true;
	for( int i=0;i<n;i++ ){
		dis[ i ] = mat[ start ][ i ];
	}
	for( int i=0;i<n;i++ ){
		int id = -1;
		double M = inf;
		for( int j=0;j<n;j++ ){
			if( vis[ j ]==false&&M>dis[ j ] ){
				M = dis[ j ];
				id = j;
			}
		}
		if( id==-1 ) break;
		vis[ id ] = true;
		ans += M;
		for( int j=0;j<n;j++ ){
			if( vis[ j ]==false&&dis[ j ]>mat[ id ][ j ] ){
				dis[ j ] = mat[ id ][ j ];
			}
		}
	}
	return ans ;
}	

int main(){
	int T;
	scanf("%d",&T);
	while( T-- ){
		int n;
		scanf("%d",&n);
		for( int i=0;i<n;i++ ){
			scanf("%lf%lf",&pnt[i].x,&pnt[i].y);
		}
		if( n==1 ){
			puts("0");
			continue;
		}
		for( int i=0;i<n;i++ ){
			for( int j=0;j<n;j++ ){
				if( i==j )
					mat[i][j] = 0.0;
				else
					mat[i][j] = dist( i,j );
			}
		}
		double res = inf; 
		for( int i=0;i<n;i++ ){
			res = min( res,Prim( (i+1)%n,i,n ) );
		}
		printf("%.2lf\n",res);
	}
	return 0;
}