UVa 10147 Highways(最小生成树，水）

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这道题，wa了，原因是没有需要建路的时候，输出一行提示，我忽视了

水题，唯一有点特别的是需要输出新建的边，那么就要建一棵前驱树，用数组表示

代码：

#include <cstdio>#include <cstring>#include <cmath>const int N = 800;const double INF = 10000000000;int T, n, m, num, p[N];double map[N][N], d[N], x[N], y[N];struct highway{    int u, v;}way[N];void prim() {    for ( int i = 0; i <= n; ++i ) d[i] = INF, p[i] = -1;    double mi;    d[1] = 0;    bool vis[N];    int v;    memset(vis, 0, sizeof(vis));    for ( int u = 0; u < n; ++u ) {        mi = INF;        for ( int i = 1; i <= n; ++i ) if ( !vis[i] && d[i] < mi ) {            v = i, mi = d[i];        }        vis[v] = true;        if ( mi > 0 ) {            printf("%d %d\n", v, p[v]);            num++;        }        for ( int i = 1; i <= n; ++i ) if ( !vis[i] && d[i] - map[v][i] > 0.0 ) {            d[i] = map[v][i];            p[i] = v;            //printf("%d %d\n", i, p[i] );        }    }}int main(){    scanf("%d", &T);    while ( T-- ) {        scanf("%d", &n);        for ( int i = 1; i <= n; ++i ) scanf("%lf%lf", &x[i], &y[i]);        for ( int i = 1; i <= n; ++i )             for ( int j = i+1; j <= n; ++j ){                 double tmp = (x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]);                map[j][i] = map[i][j] = tmp;            }        scanf("%d", &m);        while ( m-- ) {            int s,t;            scanf("%d%d", &s, &t);            map[s][t] = map[t][s] = 0;        }        num = 0;        prim();        if ( num == 0 ) printf("No new highways need\n");        if ( T > 0 ) printf("\n");    }}