HDU-1162-Eddy's picture

 

 

 

 

题目传送门：http://acm.hdu.edu.cn/showproblem.php?pid=1162

 

题意：

　　最小生成树

 

 

 

 

 

 

 

 

 

 

#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;

const int maxn = 100+10;
int far[maxn];
int n, m;
int k;
struct Edge
{
    const bool operator<(Edge &n)const 
    {
        return value<n.value;
    }
    int start;
    int end;
    double value;
}edge[maxn*maxn];

bool cmp(struct Edge &a, struct Edge &b)
{
    return a.value<b.value;
}

void init()
{
    int i, j;
    for(i=0; i<=n; i++)
        far[i] = i;
}

int find(int a)
{
    if(far[a]!=a)
        far[a] = find(far[a]);
    return far[a];
}

void Union(int a, int b)
{
    a = find(a);
    b = find(b);
    if(a != b)
        far[a] = b;
}

double kruskal()
{
    init();
    sort(edge,edge+n*(n-1)+1,cmp);
    double sum = 0;
    int count = 0;
    for(int i=1; i<=n*(n-1) && count<n; i++)  
    {
        int a=edge[i].start;
        int b=edge[i].end;
        if(find(a)!=find(b))
        {
            Union(a, b);
            sum+=edge[i].value;
            count++;
        }
    }
    return sum;
}

int main()
{
    double a[maxn], b[maxn];
    while(cin>>n)
    {
        //m = n*(n-1)/2;
        
        for(int i=1; i<=n; i++)
        {
            scanf("%lf%lf",&a[i], &b[i]);  //因为是无向图，所以要两次赋值
        }
        k=1;
        double c;
        for(int i=1; i<n; i++)
        {
            for(int j=i+1; j<=n; j++)
            {
                //if(i != j)
                //{
                    c = sqrt((a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j]));
                    edge[k].start = i;
                    edge[k].end = j;
                    edge[k++].value = c; 
                    edge[k].start = j;
                    edge[k].end = i;
                    edge[k++].value = c;
                //}
            }
        }
        printf("%.2lf\n", kruskal());
    }
    return 0;
}