hihoCoder#1098 最小生成树二·Kruscal算法

 1 #include <iostream>
 2 #include <cstdlib>
 3 
 4 using namespace std;
 5 
 6 #define MAX_EDGE 1000008
 7 #define MAX_POINT 100008
 8 
 9 struct Edge {
10   int a;
11   int b;
12   int len;
13 };
14 
15 int mycmp(const void *a, const void *b) {
16   Edge *pa = (Edge *) a;
17   Edge *pb = (Edge *) b;
18   return pa->len - pb->len;
19 }
20 
21 int N, M;
22 Edge e[MAX_EDGE];
23 int p[MAX_POINT];
24 
25 int find(int i) {
26   if (p[i] == i)
27     return i;
28   return p[i] = find(p[i]);
29 }
30 
31 void merge(int i, int j) {
32   int pi = find(i);
33   int pj = find(j);
34   p[pi] = pj;
35 }
36 
37 int kruscal() {
38   int res = 0;
39 
40   qsort(e, M, sizeof(Edge), mycmp);
41   for (int i = 0; i < M; i++) {
42     if (find(e[i].a) == find(e[i].b))
43       continue;
44     res += e[i].len;
45     merge(e[i].a, e[i].b);
46   }
47 
48   return res;
49 }
50 
51 int main() {
52   scanf("%d%d", &N, &M);
53   for (int i = 1; i <= N; i++)
54     p[i] = i;
55   for (int i = 0; i < M; i++)
56     scanf("%d%d%d", &(e[i].a), &(e[i].b), &(e[i].len));
57 
58   printf("%d\n", kruscal());
59   return 0;
60 }