学步园

题目链接：hdu 4463 Outlets

题目大意：给定N个点，以及P，Q，问说建立N-1条边联通N个点的最短长度，要求P，Q必须建立边。

解题思路：最小生成树水题。

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

using namespace std;
const int maxn = 55;

struct edge {
    double d;
    int u, v;
}ed[maxn * maxn];

int N, P, Q, E, far[maxn];
double x[maxn], y[maxn];

inline int getfar(int x) {
    return x == far[x] ? x : far[x] = getfar(far[x]);
}

inline double dis(double x, double y) {
    return sqrt(x*x+y*y);
}

inline bool cmp(const edge& a, const edge& b) {
    return a.d < b.d;
}

void init () {
    E = 0;
    scanf("%d%d", &P, &Q);

    for (int i = 1; i <= N; i++) {
        far[i] = i;
        scanf("%lf%lf", &x[i], &y[i]);
        for (int j = 1; j < i; j++)
            ed[E++] = (edge){dis(x[i]-x[j], y[i]-y[j]), i, j};
    }
    sort(ed, ed + E, cmp);
}

double solve() {
    double ret = dis(x[P]-x[Q], y[P]-y[Q]);
    far[P] = Q;

    for (int i = 0; i < E; i++) {
        int p = getfar(ed[i].u);
        int q = getfar(ed[i].v);
        if (p != q) {
            ret += ed[i].d;
            far[p] = q;
        }
    }
    return ret;
}

int main () {
    while (scanf("%d", &N) == 1 && N) {
        init();
        printf("%.2lf\n", solve());
    }
    return 0;
}