UVA10034 - Freckles(最小生成树)

UVA10034 - Freckles(最小生成树)

UVA10034 - Freckles

题目大意： 
给你n个雀斑的位置，每个雀斑看作一个点，问使得这个雀斑相互连通的最短的路径长度，最小生成树的问题。

代码：

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

const int maxn = 105;
double X[maxn], Y[maxn];
int p[maxn];

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

int getParent(int x) {
    return p[x] == x ? x : p[x] = getParent(p[x]);
}

struct Line{
    int i;
    int j;
    double d;
}l[maxn * maxn];

double dist (const int i, const int j) {
    return sqrt((X[i] - X[j]) * (X[i] - X[j]) + (Y[i] - Y[j]) * (Y[i] - Y[j]));
}

int cmp (const Line& l1, const Line& l2) {
    return l1.d < l2.d;
}

int main () {

    int T;
    scanf ("%d", &T);
    while (T--) {

        int n;
        scanf ("%d", &n);

        init(n);
        for (int i = 0; i < n; i++)
            scanf ("%lf %lf", &X[i], &Y[i]);

        int cnt = 0;
        for (int i = 0; i < n; i++)
            for (int j = i + 1; j < n; j++) {
                l[cnt].i = i;
                l[cnt].j = j;
                l[cnt++].d = dist(i, j);    
            }

        int count = 0;
        double ans = 0;
        sort(l, l + cnt, cmp);
        for (int i = 0; i < cnt; i++) {
            if (count >= n - 1)
                break;
            int p1 = getParent(l[i].i);
            int p2 = getParent(l[i].j);
            if (p1 != p2) {
                ans += l[i].d;
                p[p1] = p2;
                count++;
            }
        }

        printf ("%.2lf\n", ans);
        if (T)
            printf ("\n");
    }
    return 0;
}