Codeforces Gym 100203H Highways 最小生成树

原题链接：http://codeforces.com/gym/100203/attachments/download/1702/statements.pdf

题解

给你平面上若干点，生成一颗完全图，让你生成一颗最小生成树。模板题。图中已经有了的边要将权值置0。代码是队友写的。

代码

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <queue>
#include <map>
#include <set>
#include <vector>
#include <string>
#include <stack>
#include <bitset>
#define INF 1000000005
#define eps 1e-10
#define PI acos(-1.0)
#define K (0.017453292519943295769236907684886l)
#define LL long long
#define ULL unsigned long long

using namespace std;

const int maxn = 755;

double a[maxn][maxn], dist[maxn];

int n, pre[maxn], m, x[maxn], y[maxn], vis[maxn][maxn], flag[maxn];

double Get_dist(int s, int t)
{
    return sqrt((x[s] - x[t]) * (x[s] - x[t]) + (y[s] - y[t]) * (y[s] - y[t]));
}

int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%d%d", &x[i], &y[i]);
    memset(vis, 0, sizeof(vis));
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
             a[i][j] = Get_dist(i, j);
    scanf("%d", &m);
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        scanf("%d%d", &u, &v);
        vis[u][v] = vis[v][u] = 1;
        a[u][v] = a[v][u] = 0;
    }
    for (int i = 1; i <= n; i++)
    {
        flag[i] = 1;
        dist[i] = a[1][i];
        pre[i] = 1;
    }
    flag[1] = 0; pre[1] = 0;
    for (int i = 1; i < n; i++)
    {
        double minx = 1e30;
        int p;
        for (int j = 1; j <= n; j++)
            if (flag[j] && minx > dist[j])
            {
                minx = dist[j];
                p = j;
            }
        if (!vis[p][pre[p]]) printf("%d %d\n", p, pre[p]);
        flag[p] = 0;
        for (int j = 1; j <= n; j++)
            if (dist[j] > a[p][j])
            {
                dist[j] = a[p][j];
                pre[j] = p;
            }
    }
    return 0;
}