暴力出奇迹，搭配上O2轻松通过这道题

#include <bits/stdc++.h>
using namespace std;
const int N = 5e4 + 5;
int n, m, u, v, w, ans;
struct Node {
	int v, w;
} ;
struct P {
	int u, v, w;
	bool operator<(const P& other) const {
	    return tie(u, v, w) < tie(other.u, other.v, other.w);
	}
};
vector <Node> p[2005];
set <P> ma;
int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0' || ch>'9'){ if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0' && ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
    return x*f;
}
int main() {
    n = read(); m = read();
    while (m--) {
		u = read(); v = read(); w = read();
		p[u].push_back({v, w});
		ma.insert({u, v, w});
	}
	for (int i = 1; i <= n; ++i)
		for (int j = 0; j < p[i].size(); ++j) {
			int b = p[i][j].v, c = p[i][j].w;
			for (int k = 0; k < p[b].size(); ++k) {
				int d = p[b][k].w;
				if (c != p[b][k].v) continue;
				if (ma.find({i, b, d}) != ma.end() && ma.find({i, c, d}) != ma.end()) 
					++ans;
			}
		}
	printf("%d", ans);
    return 0;
}