HDU 1875 畅通工程再续(Kruskal + 并查集)

题目链接：HDU 1875 畅通工程再续

Kruskal + 并查集。

跟上道题类似，转化一下就好了。

#include <iostream>
#include <algorithm>
#include <iomanip>
#include <cmath>

using namespace std;

const int MAX_M = 100 + 10;
const int MAX_N  = (MAX_M * (MAX_M - 1)) >> 1;
double w[MAX_N];
int u[MAX_N],v[MAX_N],p[MAX_M],r[MAX_N];
struct Point
{
    int x,y;
};
Point point[MAX_M];

int cmp(int i,int j)
{
    return w[i] < w[j];
}
int _find(int x)
{
    return x == p[x] ? x : (p[x] = _find(p[x]));
}
double dis(int i,int j)
{
    return sqrt((point[i].x - point[j].x) * (point[i].x - point[j].x) + (point[i].y - point[j].y) * (point[i].y - point[j].y));
}
bool ok(int i,int j)
{
    double d = dis(i,j);
    if(d < 10.0 || d > 1000.0)
        return false;
    return true;
}
int C,T;
double ans;

int main()
{
    cin >> T;
    while(T--)
    {
        ans = 0.0;
        cin >> C;
        for(int i = 1;i <= C;i++)
        {
            p[i] = i;
            cin >> point[i].x >> point[i].y;
        }
        int cnt = 1;
        for(int i = 1;i <= C;i++)
        {
            for(int j = i + 1;j <= C;j++)
            {
                if(!ok(i,j))
                    continue;
                u[cnt] = i;
                v[cnt] = j;
                w[cnt] = dis(i,j);
                r[cnt] = cnt;
                cnt++;
            }
        }
        sort(r + 1,r + cnt,cmp);
        int a,b;
        for(int i = 1;i < cnt;i++)
        {
            a = _find(u[r[i]]);
            b = _find(v[r[i]]);
            if(a != b)
            {
                p[a] = b;
                C--;
                ans += w[r[i]];
            }
        }
        ans *= 100;
        if(C == 1)
            cout << fixed << setprecision(1) << ans << endl;
        else
            cout << "oh!" << endl;

    }
    return 0;
}