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+;

 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=;i<=n;i++)
         f[i]=i;
     for(int i=;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=,max_num=-;
     for(int i=;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-))
             break;
     }
     sort(edge.begin(),edge.end(),cmp1);
     for(int i=;i<=m;i++)
         f[i]=i;
     LL ans=;
     k=;
     for(int i=;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-))
             break;
     }
     cout<<ans<<endl;
     return ;
 }