思路：
倒过来用并查集。注意天数不要重复计算。
实现：
1 #include <bits/stdc++.h> 2 using namespace std; 3 const int MAXN = 10005; 4 const int MAXM = 100005; 5 int par[MAXN], n, m; 6 void init(int n) 7 { 8 for (int i = 1; i <= n; i++) par[i] = i; 9 } 10 int find(int x) 11 { 12 if (par[x] == x) return x; 13 return par[x] = find(par[x]); 14 } 15 void uni(int x, int y) 16 { 17 x = find(x); y = find(y); 18 if (x != y) par[x] = y; 19 } 20 bool same(int x, int y) 21 { 22 return find(x) == find(y); 23 } 24 struct node 25 { 26 int x, y, t; 27 }; 28 node a[MAXM]; 29 bool cmp(node & a, node & b) { return a.t > b.t; } 30 int main() 31 { 32 scanf("%d %d", &n, &m); 33 init(n); 34 for (int i = 0; i < m; i++) scanf("%d %d %d", &a[i].x, &a[i].y, &a[i].t); 35 sort(a, a + m, cmp); 36 int cnt = 0, last = -1; 37 for (int i = 0; i < m; i++) 38 { 39 if (!same(a[i].x, a[i].y) && a[i].t != last) 40 { 41 cnt++; 42 last = a[i].t; 43 } 44 uni(a[i].x, a[i].y); 45 } 46 printf("%d ", cnt); 47 return 0; 48 }