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;
}

貌似没有人提交题解，我来一个吧，发现没有题解的题通过率那么低。

#include<bits/stdc++.h>
using namespace std;
int n,m,cnt=0;
vector<int> eg[2005][2005];
bool *ex[2005][2005];
int main(){
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		int u,v,w;
		scanf("%d%d%d",&u,&v,&w);
		eg[u][v].emplace_back(w);
		if(ex[v][w]==nullptr){
			ex[v][w]=new bool[2005];
			memset(ex[v][w],0,2005);
		}
		ex[v][w][u]=1;
	}
	for(int a=1;a<n;a++)
		for(int b=a+1;b<=n;b++){
			sort(eg[a][b].begin(),eg[a][b].end());
			for(int cc=0;cc<eg[a][b].size();cc++)
				for(int dd=cc+1;dd<eg[a][b].size();dd++){
					int c=eg[a][b][cc],d=eg[a][b][dd];
					if(ex[c][d]!=nullptr && ex[c][d][a] && ex[c][d][b])
						cnt++;
				}
		}
	cout<<cnt<<endl;
	return 0;
}

代码自己理解，保证全AC