[推销博客](https://foreverlasting1202.github.io/2019/08/27/CF1208%E9%A2%98%E8%A7%A3/)
### C Magic Grid
题意：给一个$n$，需要构造一个$n*n$的矩阵，包含$0,...,n^2-1$，且每行每列的异或和相等。$4\leq n\leq 4000,4|n$。
做法：每$4*4$的为一组，显然可以构造出都为$0$的情况，复杂度$O(n^2)$。
code:
```cpp
//2019.8.24 by ljz
//email
[email protected]
//if you find any bug in my code
//please tell me
#include<bits/stdc++.h>
using namespace std;
#define res register int
#define LL long long
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f
#define unl __int128
#define eps 5.6e-8
#define RG register
#define db double
#define pc(x) __builtin_popcount(x)
typedef pair<int,int> Pair;
#define mp make_pair
#define fi first
#define se second
#define pi acos(-1.0)
#define pb push_back
#define ull unsigned LL
#define gc getchar
//inline char gc() {
// static char buf[100000],*p1,*p2;
// return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
//}
//inline int read() {
// res s=0,ch=gc();
// while(ch<'0'||ch>'9')ch=gc();
// while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
// return s;
//}
inline int read() {
res s=0,ch=gc(),w=1;
while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=gc();}
while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
return s*w;
}
inline LL Read() {
RG LL s=0;
res ch=gc();
while(ch<'0'||ch>'9')ch=gc();
while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
return s;
}
//inline LL Read() {
// RG LL s=0;
// res ch=gc(),w=1;
// while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=gc();}
// while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
// return s*w;
//}
//inline void write(RG unl x){
// if(x>10)write(x/10);
// putchar(int(x%10)+'0');
//}
inline void swap(res &x,res &y) {
x^=y^=x^=y;
}
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//clock_t start=clock();
//inline void ck(){
// if(1.0*(clock()-start)/CLOCKS_PER_SEC>0.1)exit(0);
//}
//const int N=1e6+10;
namespace MAIN{
const int N=2005;
int M[N][N],n,c;
void solve(res l,res r,res ql,res qr){for(res i=l;i<=r;i++)for(res j=ql;j<=qr;j++)M[i][j]=c++;}
inline void MAIN(){
scanf("%d",&n);
for(res i=1;i<=n>>2;i++)for(res j=1;j<=n>>2;j++)solve((i-1)*4+1,i*4,(j-1)*4+1,j*4);
for(res i=1;i<=n;i++){
for(res j=1;j<=n;j++)
printf("%d ",M[i][j]);
puts("");
}
}
}
int main(){
// srand(19260817);
// freopen("signin.in","r",stdin);
// freopen("signin.out","w",stdout);
MAIN::MAIN();
return 0;
}
```