P2872 [USACO07DEC]Building Roads S

#include <cmath>
#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 5000100;
int n, m, cnt, fa[N], sum;
double ans;
struct Node {
    int x, y;
}E[N];
struct node {
    int from, to;
    double w;
}e[N];
int read() {
    int s = 0, w = 1;
    char ch = getchar();
    while(!isdigit(ch)) {if(ch == '-') w = -1;ch = getchar();}
    while(isdigit(ch)) {s = s * 10 + ch - '0';ch = getchar();}
    return s * w;
}
void add(int x, int y, double z) {
    e[++cnt].from =x;
    e[cnt].to = y;
    e[cnt].w = z;
}
double jl(int x, int y) {
    return (double)(sqrt((double)(E[x].x - E[y].x) * (E[x].x - E[y].x) + (double)(E[x].y - E[y].y) * (E[x].y - E[y].y)));
}
bool cmp(node x, node y) {
    if(x.w == y.w) return x.from < y.from;
    return x.w < y.w;
}
int find(int x) {
    return x == fa[x] ? x : fa[x] = find(fa[x]);
}
int main() {
    n = read(), m = read();
    for(int i = 1; i <= n; i++) 
        E[i].x = read(), E[i].y = read();
    for(int i = 1; i <= n; i++) fa[i] = i;
    for(int i = 1; i <= n; i++) {
        for(int j = i + 1; j <= n; j++) {
            double z = jl(i, j);
            add(i, j, z);
        }
    }
    for(int i = 1; i <= m; i++) {
        int x = read(), y = read();
        add(x, y, 0.0);
    }
    sort(e + 1, e + 1 + cnt, cmp);
    for(int i = 1; i <= cnt; i++) {
        int fx = find(e[i].from), fy = find(e[i].to);
        if(fx != fy) {
            fa[fx] = fy;
            sum++;
            ans += e[i].w;
        }
        if(sum == n - 1) break;
    }
    printf("%.2lf
", ans);
    return 0;
}