poj3625

最小生成树

View Code

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

#define maxn 1005
#define inf 0x3f3f3f3f

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

int n, m;
long double cost[maxn][maxn];
int vis[maxn];
long double lowc[maxn];

double dist(Point &a, Point &b)
{
    Point p;
    p.x = a.x - b.x;
    p.y = a.y - b.y;
    return sqrt(p.x * p.x + p.y * p.y);
}

double prim()
{
    int i, j, p;
    long double minc, res = 0;
    memset(vis, 0, sizeof(vis));
    vis[0] = 1;
    for (i = 1; i < n; i++)
        lowc[i] = cost[0][i];
    for (i = 1; i < n; i++)
    {
        minc = inf;
        p = -1;
        for (j = 0; j < n; j++)
            if (0 == vis[j] && minc > lowc[j])
            {
                minc = lowc[j];
                p = j;
            }
        if (inf == minc)
            return -1;
        res += minc;
        vis[p] = 1;
        for (j = 0; j < n; j++)
            if (0 == vis[j] && lowc[j] > cost[p][j])
                lowc[j] = cost[p][j];
    }
    return res;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i++)
        scanf("%lld%lld", &point[i].x, &point[i].y);
    for (int i = 0; i < n; i++)
        for (int j = i + 1; j < n; j++)
            cost[i][j] = cost[j][i] = dist(point[i], point[j]);
    for (int i = 0; i < m; i++)
    {
        int a, b;
        scanf("%d%d", &a, &b);
        a--;
        b--;
        cost[a][b] = cost[b][a] = 0;
    }
    printf("%.2f\n", prim());
    return 0;
}