HDU-4081-Qin Shi Huang's National Road System

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ACM模版

描述

题解

今天第一次写次小生成树，脑子都快要炸了，写出来后测试了十几组数据（网上找了一个分AC代码进行测试对比），结果都对，对比代码部分，感觉也没有太大的差别，可是就是无法AC，无限WA，各种改，各种WA，三四个小时被这一道题给卡死了，我真的伤心透了，如果哪个大神看出来我的代码的问题了，烦请评论区告知~~~暂且Mark一下吧！！！

代码

#include <iostream>#include <cstdio>#include <cstring>#include <cmath>using namespace std;const int MAXN = 1010;struct city{    double X;    double Y;    double P;};struct city City[MAXN];double cost[MAXN][MAXN];/* *  求最小生成树时，用数组MAX[i][j]表示i到j的最大边权 *  求完后，直接枚举所有不在MST中的边，替换掉最大边权的边，更新答案 *  点的编号从0开始 */const int INF = 0x3f3f3f3f;bool vis[MAXN];double lowc[MAXN];int pre[MAXN];double MAX[MAXN][MAXN];bool used[MAXN][MAXN];double Prim(double cost[][MAXN], int n){    double ans = 0;    memset(vis, false, sizeof(vis));    memset(MAX, 0, sizeof(MAX));    memset(used, false, sizeof(used));    vis[0] = true;    pre[0] = -1;    lowc[0] = 0;    for (int i = 1; i < n; i++)    {        lowc[i] = cost[0][i];        pre[i] = 0;    }    for (int i = 1; i < n; i++)    {        double minc = INF;        int p = -1;        for (int j = 0; j < n; j++)        {            if (!vis[j] && minc > lowc[j])            {                minc = lowc[j];                p = j;            }        }        if (minc == INF)        {            return -1;        }        ans += minc;        vis[p] = true;        used[p][pre[p]] = used[pre[p]][p] = true;        for (int j = 0; j < n; j++)        {            if (vis[j])            {                MAX[j][p] = MAX[p][j] = max(MAX[j][pre[p]], lowc[p]);            }            if (!vis[j] && lowc[j] > cost[p][j])            {                lowc[j] = cost[p][j];                pre[j] = p;            }        }    }    return ans;}inline double getDis(double x, double y, double x_, double y_){    return sqrt(pow((x - x_), 2) + pow((y - y_), 2));}int main(int argc, const char * argv[]){    int T;    cin >> T;    int n;    while (T--)    {        memset(cost, 0, sizeof(cost));        cin >> n;        for (int i = 0; i < n; i++)        {            scanf("%lf%lf%lf", &City[i].X, &City[i].Y, &City[i].P);        }        for (int i = 0; i < n; i++)        {            for (int j = i + 1; j < n; j++)            {                double dis = getDis(City[i].X, City[i].Y, City[j].X, City[j].Y);                cost[i][j] = cost[j][i] = dis;            }        }        double res = Prim(cost, n);        double ans = -1;        for (int i = 0; i < n; i++)        {            for (int j = i + 1; j < n; j++)            {                if (used[i][j])                {                    ans = max(ans, (City[i].P + City[j].P) / (res - cost[i][j]));                }                else                {                    ans = max(ans, (City[i].P + City[j].P) / (res - MAX[i][j]));                }            }        }        printf("%.2lf\n", ans);    }    return 0;}

参考

《次小生成树》

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