并查集 代码：

#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 5;
int n;

struct Ufs {
	int f[maxn], sz[maxn];
	void init() {
		for (int i = 1; i <= n; i++)
			f[i] = i, sz[i] = 1;
	}
	int find(int x) {
		return x == f[x] ? x : f[x] = find(f[x]);
	}
	void merge(int x, int y) {
		int a = find(x), b = find(y);
		if (a != b) {
			f[b] = a;
			sz[a] += sz[b];
		}
	}
} tr[2];

int main() {
	scanf("%d", &n);
	tr[0].init(), tr[1].init();
	for (int i = 1; i < n; i++) {
		int u, v, c;
		scanf("%d%d%d", &u, &v, &c);
		tr[c].merge(u, v);
	}
	long long ans = 0;
	for (int u = 1; u <= n; u++) {
		for (int i = 0; i < 2; i++)
			if (tr[i].find(u) == u)
				ans += (long long) tr[i].sz[u] * (tr[i].sz[u] - 1);
		long long cnt0 = tr[0].sz[ tr[0].find(u) ];
		long long cnt1 = tr[1].sz[ tr[1].find(u) ];
		ans += (cnt0 - 1) * (cnt1 - 1);
	}
	printf("%lld\n", ans);
	return 0;
}