51 Nod 1640 天气晴朗的魔法( Kruskall )

#include <bits/stdc++.h>
typedef long long LL;
using namespace std;
const int maxn = 2e5+5;

struct node{
    LL u,v,w;
    node(){}
    node(LL a,LL b,LL c):u(a),v(b),w(c){}
};

LL f[maxn];
LL n,m;
vector<node>edge;
int Find(LL x)
{
    if (f[x] != x)
        f[x] = Find(f[x]);
    return f[x];
}

void Union(LL a, LL b)
{
    int a1 = Find(a);
    int b1 = Find(b);
    if (a1 != b1)
        f[a1] = b1;
}
bool cmp1(node a,node b)
{
    return a.w>b.w;
}
bool cmp2(node a,node b)
{
    return a.w<b.w;
}
int main()
{
    ios::sync_with_stdio(false);
    cin>>n>>m;
    for(int i=1;i<=n;i++)
        f[i]=i;
    for(int i=0;i<m;i++){
        LL a,b,c;
        cin>>a>>b>>c;
        edge.push_back(node(a,b,c));
    }
    sort(edge.begin(),edge.end(),cmp2);
    LL k=0,max_num=-1;
    for(int i=0;i<m;i++)
    {
        if(Find(edge[i].u)!=Find(edge[i].v))
        {
            Union(edge[i].u,edge[i].v);
            max_num = max(max_num,edge[i].w);
            k++;
        }
        if(k==(n-1))
            break;
    }
    sort(edge.begin(),edge.end(),cmp1);
    for(int i=1;i<=m;i++)
        f[i]=i;
    LL ans=0;
    k=0;
    for(int i=0;i<m;i++)
    {
        if(edge[i].w>max_num)continue;
        if(Find(edge[i].u)!=Find(edge[i].v))
        {
            Union(edge[i].u,edge[i].v);
            ans += edge[i].w;
            k++;
        }
        if(k==(n-1))
            break;
    }
    cout<<ans<<endl;
    return 0;
}