Out of Hay最小生成树

Out of Hay
原题链接https://vjudge.net/contest/352170#problem/D


题意为给出n个地点之间的m条路，计算链接到所以地点的最短的路中最长的一截的长度。相较于板子，增加一步判断大小，选择最大的一条路即可。
Prim:

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
long long map[3005][3005];
long long dis[300005];
bool vis[300005];
long long ans;
long long n;
long long maxx;
void prim()
{
    ans = 0;
    long long i, j;
    for (i = 1; i <= n; i++)
    {
        dis[i] = map[1][i];
        vis[i] = false;
    }
    vis[1] = true;
    for (i = 0; i < n - 1; i++)
    {
        long long minn = INF;
        long long p = 1;
        for (j = 1; j <= n; j++)
        {
            if (!vis[j] && dis[j] < minn)
            {
                minn = dis[j];
                p = j;
            }
        }
        // cout << "***" << endl;
        //  for (j = 1; j <= n; j++)
        //  {
        //      cout << dis[j] << " ";
        //   }
        //    cout << endl;
        if (minn == INF)
        {
            ans = -1;
            return;
        }
        ans += minn;
        maxx = max(maxx, minn);//选取我们选的路中最大的一条。
        vis[p] = true;
        for (j = 1; j <= n; j++)
        {
            if (!vis[j] && dis[j] > map[p][j])
            {
                dis[j] = map[p][j];
            }
        }
    }
    return;
}
int main()
{
    long long m;
    long long i, j;
    scanf("%lld %lld", &n, &m);
    for (i = 0; i <= n; i++)
    {
        for (j = 0; j <= n; j++)
        {
            map[i][j] = INF;
        }
    }
    while (m--)
    {
        long long a, b, w;
        scanf("%lld %lld %lld", &a, &b, &w);
        if (w < map[a][b])//尤其要注意读取地图只要最小的一条路，因为这个wa了3发，Emmmm.
        {
            map[a][b] = w;
        }
        if (map[b][a] > w)
        {
            map[b][a] = w;
        }
    }
    maxx = -1;
    prim();
    cout << maxx << endl;
    return 0;
}

Kruskal:

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <queue>
using namespace std;
long long pre[300005];
long long map[3005][3005];
struct node
{
	long long u;
	long long v;
	long long w;
} stu[300005];
long long ans;
long long cnt;
long long maxx;
bool cmp(node x, node y)
{
	return x.w < y.w;
}
long long find(long long x)
{
	if (x == pre[x])
	{
		return x;
	}
	return pre[x] = find(pre[x]);
}
void join(long long x, long long y, long long w)
{
	long long ss1 = find(x);
	long long ss2 = find(y);
	if (ss1 != ss2)
	{
		pre[ss2] = ss1;
		ans += w;
		maxx = max(maxx, w);//选取最长的一条路。
		cnt--;
	}
}
int main()
{
	long long n, i, m;
	scanf("%lld %lld", &n, &m);
	ans = 0;
	cnt = n;
	for (i = 0; i <= n; i++)
	{
		pre[i] = i;
	}
	for (i = 0; i < m; i++)
	{
		scanf("%lld %lld %lld", &stu[i].u, &stu[i].v, &stu[i].w);
	}
	sort(stu, stu + m, cmp);
	/*	for (i = 0; i < k; i++)
	{
		printf("*%lld %lld %lld\n", stu[i].u, stu[i].v, stu[i].w);
	}
	for (i = 0; i <= n;i++)
	{
		cout << pre[i] << endl;
	}
		cout << endl;*/
	maxx = -1;
	for (i = 0; i < m; i++)
	{
		join(stu[i].u, stu[i].v, stu[i].w);
		if (cnt == 1)
		{
			break;
		}
	}
	if (cnt > 1)
	{
		ans = -1;
	}
	cout << maxx << endl;
	return 0;
}