AC代码：

#include <iostream>
#include <algorithm>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#define LL long long 
#define ULL unsigned long long
using namespace std;
//typedef long long LL;

const int N = 505;

const int mod = 100000000;
int n;

/*void mul(LL a[][N+1], LL b[][N+1], LL c[][N+1]) {
static LL tmp[N+1][N+1];
for(int i = 1;i <= n;i++){
for(int j = 1;j <= n;j++){
tmp[i][j] = 0;
}
}
for(int k = 1;k <= n;k++)
for(int i = 1;i <= n;i++)
for(int j = 1;j <= n;j++)
tmp[i][j] = (ULL)(tmp[i][j] + a[i][k] * b[k][j]);

for(int i = 1;i <= n;i++)
for(int j = 1;j <= n;j++)
c[i][j] = tmp[i][j];//cpy
}*/

/*void fpow(LL a[][N+1], LL k, LL res[][N+1]) {
for(int i = 1;i <= N;i++) {
for(int j = 1;j <= N;j++){
//TODO
res[i][j] = 0;
}
}
for(int i = 1;i <= N;i++) {
res[i][i] = 1;
}
LL tmb[N+1][N+1];
for(int i = 1;i <= N;i++) {
for(int j = 1;j <= N;j++) {
tmb[i][j] = a[i][j];
}
}

while(k) {
if(k & 1) mul(res, tmb, res);
k >>= 1;
mul(tmb, tmb, tmb);
}
}*/

/*bool cp(LL x[N+1][N+1], LL y[N+1][N+1]){
//bool dick = 1;
for(int i = 1;i <= n;i++) {
for(int j = 1;j <= n;j++) {
if(x[i][j] != y[i][j]){
return 0;
}
}
}
return 1;
}*/

void mul_vec(LL m[][N+1], LL vec[], LL out[]) {
	//memset(out, 0, sizeof(LL) * (N+1));
	fill(out, out + N + 1, 0);
	for(int i = 1;i <= n;i++) 
		for(int k = 1;k <= n;k++)
			out[i] += (ULL)(m[i][k]) * (vec[k]);
}

LL aa[N+1][N+1], bb[N+1][N+1], cc[N+1][N+1];
LL pre_[N+1][N+1];

LL x[N+1], L[N + 1], R[N+1], rr[N+1];
bool check() {
	for(int i = 1;i <= n;i++) {
		ULL val = (ULL)rand() * rand();
		rr[i] = val;
	}
	
	//memset(x,0,sizeof(x));
	//memset(L, 0, sizeof(L));
	//memset(R, 0, sizeof(R));
	
	mul_vec(bb, rr, x);
	mul_vec(aa, x, L);
	mul_vec(cc, rr, R);
	
	
	
	
	bool is_d = 1;
	for(int i = 1;i <= n;i++){
		if(L[i] != R[i]){
			is_d = 0;
			break;
		}
	}
	return is_d;
}


int main() {
	srand(time(0));
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	
	while(cin >> n){
		/*memset(aa, 0, sizeof(aa));
		memset(bb, 0, sizeof(bb));
		memset(cc, 0, sizeof(cc));
		memset(pre_, 0, sizeof(pre_));*/
		
		
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> aa[i][j];
			}
		}
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> bb[i][j];
			}
		}
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> cc[i][j];
			}
		}
		
		
		/*for(int i = 1;i <= n;i++)
		for(int j = 1;j <= n;j++)
		pre_[i][j] = 0;
		mul(aa, bb, pre_);
		bool ans = cp(pre_, cc);
		if(ans) cout << "YES\n";
		else cout << "NO\n";*/
		bool ans = 1;
		for(int t = 0;t < 15;t++) {
			if(!check()){
				ans = 0;
				break;
			}
		}
		if(ans) cout << "YES\n";
		else cout << "NO\n";
	}
	return 0;
}

WA代码：

#include <iostream>
#include <string.h>//Different Point 1#
#include <stdlib.h>
#include <time.h>
#define LL long long 
using namespace std;
//typedef long long LL;

const int N = 505;

const int mod = 2009;//Different Point 2#
int n;

void mul(LL a[][N+1], LL b[][N+1], LL c[][N+1]) {//Diffierent Point 3#:AC代码已注释无关函数模板;
	static LL tmp[N+1][N+1];
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= n;j++){
			tmp[i][j] = 0;
		}
	}
	for(int k = 1;k <= n;k++)
		for(int i = 1;i <= n;i++)
			for(int j = 1;j <= n;j++)
				tmp[i][j] = (tmp[i][j] + a[i][k] * b[k][j]);
	
	for(int i = 1;i <= n;i++)
		for(int j = 1;j <= n;j++)
			c[i][j] = tmp[i][j];//cpy
}

void fpow(LL a[][N+1], LL k, LL res[][N+1]) {
	for(int i = 1;i <= N;i++) {
		for(int j = 1;j <= N;j++){
			//TODO
			res[i][j] = 0;
		}
	}
	for(int i = 1;i <= N;i++) {
		res[i][i] = 1;
	}
	LL tmb[N+1][N+1];
	for(int i = 1;i <= N;i++) {
		for(int j = 1;j <= N;j++) {
			tmb[i][j] = a[i][j];
		}
	}
	
	while(k) {
		if(k & 1) mul(res, tmb, res);
		k >>= 1;
		mul(tmb, tmb, tmb);
	}
}

bool cp(LL x[N+1][N+1], LL y[N+1][N+1]){
	//bool dick = 1;
	for(int i = 1;i <= n;i++) {
		for(int j = 1;j <= n;j++) {
			if(x[i][j] != y[i][j]){
				return 0;
			}
		}
	}
	return 1;
}//注释结束

void mul_vec(LL m[][N+1], LL vec[], LL out[]) {
	memset(out, 0, sizeof(LL) * (N+1));//Diffierent Point 4#:换memset为fill;
	
	for(int i = 1;i <= n;i++) 
		for(int k = 1;k <= n;k++)
			out[i] = (out[i] + (m[i][k] % mod) * (vec[k] % mod) ) % mod + mod;//Diffierent Point 5#:增加ULL自然溢出，删除取模操作
}

LL aa[N+1][N+1], bb[N+1][N+1], cc[N+1][N+1];
LL pre_[N+1][N+1];

bool check() {
	
	LL rr[N+1];
	for(int i = 1;i <= n;i++) {
		rr[i] = 1LL * rand() * rand() % 200000 - 100000;
	}
	//Diffierent Point 6#:将x, y, z设为全局数组
	LL x[N+1];
	memset(x,0,sizeof(x));
	mul_vec(bb, rr, x);
	
	LL L[N + 1];
	memset(L, 0, sizeof(L));
	mul_vec(aa, x, L);
	
	LL R[N+1];
	memset(R, 0, sizeof(R));
	mul_vec(cc, rr, R);
	
	bool is_d = 1;
	for(int i = 1;i <= n;i++){
		if(L[i] != R[i]){
			is_d = 0;
			break;
		}
	}
	return is_d;
}


int main() {
	srand(time(0));
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	
	
	while(cin >> n){
		/*memset(aa, 0, sizeof(aa));
		memset(bb, 0, sizeof(bb));
		memset(cc, 0, sizeof(cc));
		memset(pre_, 0, sizeof(pre_));*/
		
		
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> aa[i][j];
			}
		}
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> bb[i][j];
			}
		}
		for(int i = 1;i <= n;i ++) {
			for(int j = 1;j <= n;j ++) {
				cin >> cc[i][j];
			}
		}
		
		
		/*for(int i = 1;i <= n;i++)
		for(int j = 1;j <= n;j++)
		pre_[i][j] = 0;
		mul(aa, bb, pre_);
		bool ans = cp(pre_, cc);
		if(ans) cout << "YES\n";
		else cout << "NO\n";*/
		bool ans = 1;
		for(int t = 0;t < 10;t++) {//Diffierent Point 7#:哈希增加至15；
			if(!check()){
				ans = 0;
				break;
			}
		}
		if(ans) cout << "YES\n";
		else cout << "NO\n";
	}
	return 0;
}

核心错因：Diffierent 5 取模操作错误，逻辑出现故障。