题解 | Freckles

#include <stdio.h>
#include<string.h>
#include<math.h>
//最小生成树
typedef struct Graph {
    double edges[200][200];
    int v_num, e_num; //顶点数和边数量
} Graph;
double Prim(Graph g, int v) {
    double sum = 0;
    double lowcost[100];
    double mindist;
    int closet[100], i, j, k;
    for ( i = 0; i < g.v_num; i++) { //将lowcost与closet数组初始化
        lowcost[i] = g.edges[v][i];
        closet[i] = v;
    }
    for ( i = 1; i < g.v_num; i++) { //从U-V中找到离U中的点最近的点
        mindist = 1.79769e+308;
        for ( j = 0; j < g.v_num; j++) {
            if (lowcost[j] != 0 && lowcost[j] < mindist) {
                mindist = lowcost[j];
                k = j;
            }
        }
        // printf("边（%d %d）权值为%f\n",closet[k],k,mindist);
        lowcost[k] = 0;//将k点并入U中
        for ( j = 0; j < g.v_num;
                j++) { //将lowcost数组与closet数组更新，若U-V集合到新并入的点的距离更新
            // 就将lowcost中对应的距离更新，将closet中所对应的点也随之更新
            if (lowcost[j] != 0 && g.edges[k][j] < lowcost[j]) {
                lowcost[j] = g.edges[k][j];
                closet[j] = k;
            }

        }
        sum = sum + mindist;
    }
    printf("%.2lf", sum);
    return sum;
}
double EuclideanD(double x_1, double y_1, double x_2, double y_2) {
    return sqrt((x_1 - x_2) * (x_1 - x_2) + (y_1 - y_2) * (y_1 - y_2));
}

int main() {
    int e_num, v_num;
    Graph g;
    int n;
    scanf("%d", &n);
    double X[100], Y[100];
    for (int i = 0; i < n; i++) {
        scanf("%lf %lf", &X[i], &Y[i]); //输入每个点的坐标
        // printf("%lf %lf",X[i],Y[i]);
    }
    // printf("%d\n",n);
    g.v_num = n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (i == j) {
                g.edges[i][j] = 0;
            } else {
                double D;
                D = EuclideanD(X[i], Y[i], X[j], Y[j]);
                g.edges[i][j] = D;
                // printf("%lf  ",D);
            }
        }
    }
    // for (int i = 0; i < n; i++)
    // {
    //     for (int j = 0; j < n; j++)
    //     {
    //         printf("%lf  ",g.edges[i][j]);
    //     }
    //     printf("\n");
    // }
    Prim(g, 0);
    return 0;
}