/*
最小生成树 之 CODE[VS] 1231 最优布线问题
Kruskal算法（邻接表）
*/
1 #include <iostream>
2 #include <cstdlib>
3 #include <cstdio>
4 #include <cstddef>
5 #include <iterator>
6 #include <algorithm>
7 #include <string>
8 #include <locale>
9 #include <cmath>
10 #include <vector>
11 #include <cstring>
12 #include <map>
13 #include <utility>
14 #include <queue>
15 #include <stack>
16 #include <set>
17 #include <functional>
18 using namespace std;
19 typedef pair<int, int> PII;
20 typedef long long int64;
21 const int INF = 0x3f3f3f3f;
22 const int modPrime = 3046721;
23 const double eps = 1e-9;
24 const int MaxN = 100010;
25 const int MaxM = 100010;
26
27
28
29 /***************************************************/
30 /*Union-find sets*/
31 int ftr[MaxN];
32 int rnk[MaxN];
33
34 void ufsIni(int n)
35 {
36 for (int i = 0; i <= n; ++i)
37 {
38 ftr[i] = i;
39 rnk[i] = 0;
40 }
41 }
42
43 int ufsFind(int x)
44 {
45 if (x == ftr[x]) return x;
46 return ftr[x] = ufsFind(ftr[x]);
47 }
48
49 void ufsUnion(int x, int y)
50 {
51 x = ufsFind(x);
52 y = ufsFind(y);
53 if (x == y) return;
54
55 if (rnk[x] < rnk[y])
56 {
57 ftr[x] = y;
58 }
59 else
60 {
61 ftr[y] = x;
62 if (rnk[x] == rnk[y])
63 {
64 ++rnk[x];
65 }
66 }
67 }
68
69 bool ufsSame(int x, int y)
70 {
71 return (ufsFind(x) == ufsFind(y));
72 }
73
74 /***************************************************/
75
76 int N, M;
77 struct Edge
78 {
79 int u, v, cost;
80 };
81
82 bool Cmp(const Edge e1, const Edge e2)
83 {
84 return e1.cost < e2.cost;
85 }
86 Edge edge[MaxM];
87
88
89 void Solve()
90 {
91 ufsIni(N);
92 sort(edge, edge + M, Cmp);
93 int64 ans = 0;
94 for (int i = 0; i < M; ++i)
95 {
96 Edge eg = edge[i];
97 if (!ufsSame(eg.u, eg.v))
98 {
99 ufsUnion(eg.u, eg.v);
100 ans += eg.cost;
101 }
102 }
103 printf("%lld\n", ans);
104 }
105
106 int main()
107 {
108 #ifdef HOME
109 freopen("in", "r", stdin);
110 //freopen("out", "w", stdout);
111 #endif
112
113 scanf("%d %d", &N, &M);
114 for (int i = 0; i < M; ++i)
115 {
116 scanf("%d %d %d", &edge[i].u, &edge[i].v, &edge[i].cost);
117 }
118
119 Solve();
120
121 #ifdef HOME
122 cerr << "Time elapsed: " << clock() / CLOCKS_PER_SEC << " ms" << endl;
123 _CrtDumpMemoryLeaks();
124 #endif
125 return 0;
126 }
