Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của ladpro98

#include <bits/stdc++.h>
const int N = 1001;
const int lim = 5;

using namespace std;
struct mat2D {
    char mat[N][N];
};
struct mat1D {
    char mat[N];
};
mat1D bb, cc, d;
mat2D a, b, c;
int n;
char s[N];

mat1D operator * (mat2D a, mat1D b) {
    mat1D c; int i, j;
    for(i = 0; i < n; i++) c.mat[i] = 0;
    for(i = 0; i < n; i++) for(j = 0; j < n; j++)
        c.mat[i] = (c.mat[i] + a.mat[i][j] * b.mat[j]) % 10;
    return c;
}

bool ok() {
    //return true if bb = cc
    for(int i = 0; i < n; i++)
        if (bb.mat[i] != cc.mat[i]) return false;
    return true;
}

int main()
{
    int t, i, j, cnt; bool same; char ch;
    srand(time(NULL));
    scanf("%d\n", &t);
    while (t--) {
        scanf("%d\n", &n);
        for(i = 0; i < n; i++) {
            scanf("%s\n", s);
            for(j = 0; j < n; j++)
                a.mat[i][j] = s[j] - '0';
        }
        for(i = 0; i < n; i++) {
            scanf("%s\n", s);
            for(j = 0; j < n; j++)
                b.mat[i][j] = s[j] - '0';
        }
        for(i = 0; i < n; i++) {
            scanf("%s\n", s);
            for(j = 0; j < n; j++)
                c.mat[i][j] = s[j] - '0';
        }
        same = true;
        for(cnt = 0; cnt < lim; cnt++) {
            for(i = 0; i < n; i++) d.mat[i] = rand() % 10;
            bb = b * d; bb = a * bb; cc = c * d;
            //A * B = C <=> A * (B * D) = C * D
            if (!ok()) {
                same = false; break;
            }
        }
        if (same) printf("YES\n"); else printf("NO\n");
    }
    return 0;
}

Code mẫu của RR

#include <sstream>
#include <iomanip>
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <deque>
#include <complex>

#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; i--)
#define REP(i,a) for(int i=0,_a=(a); i<_a; i++)
#define FORN(i,a,b) for(int i=(a),_b=(b);i<_b;i++)
#define DOWN(i,a,b) for(int i=a,_b=(b);i>=_b;i--)
#define SET(a,v) memset(a,v,sizeof(a))
#define sqr(x) ((x)*(x))
#define ll long long
#define F first
#define S second
#define PB push_back
#define MP make_pair

#define DEBUG(x) { cout << #x << " = "; cout << x << endl; }
#define PR(a,n) { cout << #a << " = "; FOR(_,1,n) cout << a[_] << ' '; cout << endl; }
#define PR0(a,n) { cout << #a << " = "; REP(_,n) cout << a[_] << ' '; cout << endl; }
using namespace std;

//Buffer reading
int INP,AM,REACHEOF;
const int BUFSIZE = (1<<12) + 17;
char BUF[BUFSIZE+1], *inp=BUF;
#define GETCHAR(INP) { \
    if(!*inp && !REACHEOF) { \
        memset(BUF,0,sizeof BUF);\
        int inpzzz = fread(BUF,1,BUFSIZE,stdin);\
        if (inpzzz != BUFSIZE) REACHEOF = true;\
        inp=BUF; \
    } \
    INP=*inp++; \
}
#define DIG(a) (((a)>='0')&&((a)<='9'))
#define GN(j) { \
    AM=0;\
    GETCHAR(INP); while(!DIG(INP) && INP!='-') GETCHAR(INP);\
    if (INP=='-') {AM=1;GETCHAR(INP);} \
    j=INP-'0'; GETCHAR(INP); \
    while(DIG(INP)){j=10*j+(INP-'0');GETCHAR(INP);} \
    if (AM) j=-j;\
}
//End of buffer reading

const long double PI = acos((long double) -1.0);
const int MN = 1011;
const int MOD = 10;

int n, a[MN][MN], b[MN][MN], c[MN][MN], t[MN], x[MN], y[MN], z[MN];

bool check() {
    REP(turn,5) {
        FOR(i,1,n) t[i] = rand() % MOD;

        FOR(i,1,n) {
            x[i] = 0;
            FOR(j,1,n) x[i] = (x[i] + b[i][j] * t[j]) % MOD;
        }

        FOR(i,1,n) {
            y[i] = 0;
            FOR(j,1,n) y[i] = (y[i] + a[i][j] * x[j]) % MOD;
        }

        FOR(i,1,n) {
            z[i] = 0;
            FOR(j,1,n) z[i] = (z[i] + c[i][j] * t[j]) % MOD;
        }

        FOR(i,1,n) if (z[i] != y[i]) return false;
    }
    return true;
}

char tmp[1011];

int main() {
    int ntest; scanf("%d", &ntest);
    while (ntest--) {
        scanf("%d\n", &n);
        FOR(i,1,n) {
            gets(tmp);
            FOR(j,1,n) a[i][j] = tmp[j-1] - '0';
        }
        FOR(i,1,n) {
            gets(tmp);
            FOR(j,1,n) b[i][j] = tmp[j-1] - '0';
        }
        FOR(i,1,n) {
            gets(tmp);
            FOR(j,1,n) c[i][j] = tmp[j-1] - '0';
        }

        if (check()) puts("YES"); else puts("NO");
    }
    return 0;
}

Code mẫu của skyvn97

#include<cstdio>
#include<cstdlib>
#include<vector>
#define MAX   1111
#define FOR(i,a,b) for (int i=(a);i<=(b);i=i+1)
#define REP(i,n) for (int i=0;i<(n);i=i+1)
using namespace std;
struct matrix {
    int m,n;
    vector<vector<int> > d;
    matrix() {
        m=n=0;
    }
    matrix(int m,int n) {
        this->m=m;
        this->n=n;
        d.assign(m,vector<int>(n,0));
    }
    matrix operator * (const matrix &a) const {
        int x=m;
        int y=n;
        int z=a.n;
        matrix res=matrix(x,z);
        REP(i,x) REP(j,z) REP(k,y) res.d[i][j]=(res.d[i][j]+d[i][k]*a.d[k][j])%10;
        return (res);
    }
    bool operator == (const matrix &a) const {
        REP(i,m) REP(j,n) if (d[i][j]!=a.d[i][j]) return (false);
        return (true);
    }
};
char a[MAX][MAX],b[MAX][MAX],c[MAX][MAX];
int n;
matrix A,B,C;
inline int nextInt(void) {
    int x;
    scanf("%d",&x);
    return (x);
}
void init(void) {
    n=nextInt();
    REP(i,n) scanf("%s",a[i]);
    REP(i,n) scanf("%s",b[i]);
    REP(i,n) scanf("%s",c[i]);
    A=matrix(n,n);
    B=matrix(n,n);
    C=matrix(n,n);
    REP(i,n) REP(j,n) {
        A.d[i][j]=a[i][j]-48;
        B.d[i][j]=b[i][j]-48;
        C.d[i][j]=c[i][j]-48;
    }
}
bool check(void) {
    matrix R=matrix(n,1);
    REP(i,n) R.d[i][0]=rand()&1;
    return (A*(B*R)==C*R);
}
void process(void) {
    REP(zz,7) if (!check()) {
        printf("NO\n");
        return;
    }
    printf("YES\n");
}
int main(void) {
    int t=nextInt();
    srand(t);
    REP(zz,t) {
        init();
        process();
    }
    return 0;
}