hdu 1162 Eddy's picture(最小生成树Prim算法)

/*
Author: ACb0y
Date: 2010-9-15
Type: graph(MST prim)
ProblemId: hdu 1162 Eddy's picture
Result: AC
*/
#include <iostream>
#include <cmath>
using namespace std;
#define inf 99999999999.9

struct Point {
double x;
double y;
};

//顶点数
int n;
//用来保存每个顶点的坐标
Point points[110];
//用邻接矩阵保存图
double g[110][110];
//记录第一个顶点到各个顶点的最小距离
double d[110];
//用来标记顶点是否进入了最小生成树的点的集合
int vis[110];

double dis(Point a, Point b) {
return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

//最小生成树prim算法
void MST() {
int i, j;
for (i = 1; i <= n; i++) {
d[i] = inf;
}
d[1] = 0;
double ans = 0;
memset(vis, 0, sizeof(vis));
//n个顶点分别入生成树
for (i = 1; i <= n; i++) {
double Min = inf;
int pos = -1;
//查询当前最小的没有入生成树的最小的边
for (j = 1; j <= n; j++) if (!vis[j]) {
if (d[j] < Min) {
Min = d[j];
pos = j;
}
}
//标记顶点入生成树
vis[pos] = 1;
//记录代价
ans += Min;
//更新各个顶点到生成树的距离
for (j = 1; j <= n; j++) {
if (g[pos][j] < d[j]) {
d[j] = g[pos][j];
}
}
}
printf("%.2lf/n", ans);
}

int main()
{
int i, j;
#ifndef ONLINE_JUDGE
freopen("1162.txt", "r", stdin);
#endif
while (cin >> n) {
for (i = 1; i <= n; i++) {
cin >> points[i].x >> points[i].y;
}
for (i = 1; i <= n; i++) {
for (j = i; j <= n; j++) {
g[i][j] = g[j][i] = dis(points[i], points[j]);
}
}
MST();
}
return 0;
}