UVA 10397 - Connect the Campus

最小生成树问题，注意消去固定边时的方法：

#include<stdio.h>

#include<string.h>

#include<stdlib.h>

#include<math.h>

#define MAXN 800

#define MAXN1 300000



double x[MAXN], y[MAXN], w[MAXN1];

int n, p1, m, p[MAXN], u[MAXN1], v[MAXN1], r[MAXN1], vis[1010][1010];



int cmp(const void *_i, const void *_j)

{

    int *i = (int *)_i;

    int *j = (int *)_j;

    return w[*i] > w[*j] ? 1 : -1;

}

int find(int x) {return p[x] == x ? x : p[x] = find(p[x]);}

double kruskal()

{

    double ans = 0;

    for(int i = 0; i <= n; i ++) p[i] = i;

    for(int i = 0; i < p1; i ++) r[i] = i;

    qsort(r,p1,sizeof(r[0]),cmp);

    for(int i = 0; i < p1; i ++)

    {

        int e = r[i]; int x1 = find(u[e]); int y1 = find(v[e]);

        if(x1 != y1){ans += w[e]; p[x1] = y1;}

    }

    return ans;

}



void init()

{

    while(~scanf("%d",&n))

    {

        memset(vis,0,sizeof(vis));

        for(int i = 1; i <= n; i ++)

            scanf("%lf%lf",&x[i], &y[i]);

        scanf("%d",&m);

        for(int i = 0; i < m; i ++)

        {

            int z, c;

            scanf("%d%d",&z, &c);

            if(z > c) vis[c][z] = 1;

            else vis[z][c] = 1;

        }

        p1 = 0;

        for(int i = 1; i <= n; i ++)

        {

            for(int j = i+1; j <= n; j ++)

            {

                if(vis[i][j]) w[p1] = 0;

                else    

                    w[p1] = sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));

                u[p1] = i;

                v[p1] = j;

                p1 ++;

            }

        }

        printf("%.2f\n",kruskal());

    }

}

int main()

{

    init();

    return 0;

}