专题四 · 1002

代码及解释

#include <algorithm>#include <cmath>#include <cstdio>#include <iostream>// kruskal 求最小生成树，用到并查集struct Node {  int x, y;  double cost;} g[5005];int pre[105];int find(int n) { return n == pre[n] ? n : find(pre[n]); }bool cmp(Node a, Node b) { return a.cost < b.cost; }int main() {  int n;  while (scanf("%d", &n) != EOF) {    int k = 0;    double sum = 0;    double x[105], y[105];    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++) {        g[k].x = i;        g[k].y = j;        g[k++].cost = sqrt(fabs((x[i] - x[j]) * (x[i] - x[j]) +                                (y[i] - y[j]) * (y[i] - y[j])));      }    for (int i = 1; i <= n; i++)      pre[i] = i;    std::sort(g, g + k, cmp);    for (int i = 0; i < k; i++) {      int x = find(g[i].x);      int y = find(g[i].y);      double z = g[i].cost;      if (x != y) {        sum += z;        pre[x] = y;      }    }    printf("%.2f\n", sum);  }  return 0;}