UVa 10397 - Connect the Campus

/*UVa 10397 - Connect the Campus
* 把已存在的边权设为0 然后使用Kruscal算法 求最小生成树
* */
import java.util.Arrays;
import java.util.Comparator;
import java.util.Scanner;
class Edge {
int u;// 边的起点
int v;// 边的终点
double w;// 边的权重；

public Edge(int u, int v, double w) {
this.u = u;
this.v = v;
this.w = w;
}
}

class EdgeComparator implements Comparator<Edge> {
@Override
public int compare(Edge o1, Edge o2) {
if (o1.w < o2.w)
return -1;
else if (o1.w > o2.w)
return 1;
return 0;
}
}

class Main {
static final int MAXN = 760;
Edge[] e = new Edge[MAXN * MAXN];
int[] p = new int[MAXN * MAXN];
double[][] w = new double[MAXN][MAXN];
int[] x = new int[MAXN];
int[] y = new int[MAXN];

public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
Main mm = new Main();
while (scanner.hasNext()) {
int n = scanner.nextInt();
for (int i = 1; i <= n; i++) {
mm.x[i] = scanner.nextInt();
mm.y[i] = scanner.nextInt();
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= i; j++) {
if (i != j)
mm.w[i][j] = mm.w[j][i] = mm.getLength(i, j);
}
}
int m = scanner.nextInt();
for (int i = 0; i < m; i++) {
int u = scanner.nextInt();
int v = scanner.nextInt();
mm.w[u][v] = mm.w[v][u] = 0;
}
int index = 0;
for (int i = 1; i <= n; i++) {
for (int j = i + 1; j <= n; j++) {
mm.e[index++] = new Edge(i, j, mm.w[i][j]);
}
}
for (int i = 0; i <= n * n; i++) {// 并查集初始化
mm.p[i] = i;
}
double ans = 0;
Arrays.sort(mm.e, 0, index, new EdgeComparator());// 按边权排序
for (int i = 0; i < index; i++) {
int x = mm.find(mm.e[i].u);//起点
int y = mm.find(mm.e[i].v);//终点
if (x != y) {// 如果不在同一个集合就合并
ans += mm.e[i].w;
mm.p[x] = y;
}
}
System.out.printf("%.2f\n", ans);
}
}

private double getLength(int i, int j) {
double m = Math.pow(x[i] - x[j], 2);
double n = Math.pow(y[i] - y[j], 2);
return Math.sqrt(m + n);
}

private int find(int x) {
if (p[x] == x)
return x;
return p[x] = find(p[x]);
}
}