poj2560

最小生成树

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define maxn 105

struct Point
{
    double x, y;
} point[maxn];

double cost[maxn][maxn];
int n;

double dis(int a, int b)
{
    return sqrt((point[a].x - point[b].x) * (point[a].x - point[b].x) + (point[a].y
            - point[b].y) * (point[a].y - point[b].y));
}

void makecost()
{
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            cost[i][j] = dis(i, j);
}

double prim()
{
    double lowcost[maxn];
    bool vis[maxn];

    memset(vis, 0, sizeof(vis));
    for (int i = 0; i < n; i++)
        lowcost[i] = -1;
    lowcost[0] = 0;
    vis[0] = true;
    int pre = 0;
    double ans = 0;
    while (1)
    {
        for (int i = 0; i < n; i++)
            if (lowcost[i] > lowcost[pre] + cost[i][pre] || lowcost[i] == -1)
                lowcost[i] = lowcost[pre] + cost[i][pre];
        int best = 1000000000;;
        pre = -1;
        for (int i = 0; i < n; i++)
            if (!vis[i] && lowcost[i] < best)
            {
                best = lowcost[i];
                pre = i;
            }
        if (pre == -1)
            break;
        ans += lowcost[pre];
        vis[pre] = true;
        lowcost[pre] = 0;
    }
    return ans;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d", &n);
    for (int i = 0; i < n; i++)
        scanf("%lf%lf", &point[i].x, &point[i].y);
    makecost();
    printf("%.2f\n", prim());
    return 0;
}