51nod 天气晴朗的魔法 - (Kruskall最小生成树)

 1 #include<iostream>
 2 #include<cstring>
 3 #include<algorithm>
 4 
 5 typedef long long LL;
 6 using namespace std;
 7 const int maxn=200005;
 8 struct node{
 9     LL u,v,w;
10 }edge[maxn];
11 LL f[maxn];
12 LL n,m;
13 
14 int Find(LL x)
15 {
16     if (f[x] != x)
17         f[x] = Find(f[x]);
18     return f[x];
19 }
20 
21 void Union(LL a, LL b)
22 {
23     int a1 = Find(a);
24     int b1 = Find(b);
25     if (a1 != b1)
26         f[a1] = b1;
27 }
28 bool cmp1(node a,node b)
29 {
30     return a.w>b.w;
31 }
32 bool cmp2(node a,node b)
33 {
34     return a.w<b.w;
35 }
36 int main()
37 {
38     ios::sync_with_stdio(false);
39     cin>>n>>m;
40     for(int i=1;i<=n;i++)
41         f[i]=i;
42     for(int i=0;i<m;i++)
43         cin>>edge[i].u>>edge[i].v>>edge[i].w;
44     sort(edge,edge+m,cmp2);
45     LL k=0,max_num=-1;
46     for(int i=0;i<m;i++)
47     {
48         if(Find(edge[i].u)!=Find(edge[i].v))
49         {
50             Union(edge[i].u,edge[i].v);
51             max_num = max(max_num,edge[i].w);
52             k++;
53         }
54         if(k==(n-1))
55             break;
56     }
57     sort(edge,edge+m,cmp1);
58     for(int i=1;i<=m;i++)
59         f[i]=i;
60     LL ans=0;
61     k=0;
62     for(int i=0;i<m;i++)
63     {
64         if(edge[i].w>max_num)continue;
65         if(Find(edge[i].u)!=Find(edge[i].v))
66         {
67             Union(edge[i].u,edge[i].v);
68             ans += edge[i].w;
69             k++;
70         }
71         if(k==(n-1))
72             break;
73     }
74     cout<<ans<<endl;
75     return 0;
76 }