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;
}