①Kruskal算法：

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题目地址：畅通工程再续

①Kruskal算法：

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int maxn = 110;
const int MAX = 10010;
int fa[maxn];

struct Node //建立坐标
{
    double x;  //不用double会WA！！
    double y;
}a[maxn];

struct Edge //建立权值
{
    int u;
    int v;
    double len;
}b[MAX];

void init(int n)  //初始化根节点
{
    for(int i = 0; i < n; i++)
        fa[i] = i;
}
int Find(int x) //寻找根节点
{
    int r = x;
    while(fa[r] != r) {
        r = fa[r];
    }
    return r;
}
int cmp(Edge x, Edge y)  //根据权值从小到大排序
{
    return x.len < y.len;
}
bool join(int x, int y)
{
    int fx = Find(x);
    int fy = Find(y);
    if(fx != fy) {
        fa[fx] = fy;
        return true;
    }
    else
        return false;
}

int main()
{
    int t, n;
    cin >> t;
    while(t--) {
        cin >> n;
        int num = 1;
        double sum = 0;
        init(n);

        for(int i = 0; i < n; i++) {
            scanf("%lf%lf", &a[i].x, &a[i].y);
        }
        //建图
        int i , j, k;
        for(i = 0, k = 0; i < n; i++) {
            for(j = i+1; j < n; j++) {
                b[k].u = i;
                b[k].v = j;
                b[k].len = sqrt(pow(a[i].x - a[j].x, 2) + pow(a[i].y - a[j].y, 2));
                k++;
            }
        }
        sort(b, b + k, cmp);
        for(i = 0; i < k; i++) {
            if(b[i].len >= 10 && b[i].len <= 1000) {
                if(join(b[i].u, b[i].v)) {
                    sum += b[i].len;
                    num++;
                }
            }
        }
        if(num == n) {
            printf("%.1lf\n", sum*100);
        }
        else
            printf("oh!\n");
    }
    return 0;
}