- #include<cstdio>
- #include<iostream>
- #include<string>
- #include<vector>
- #include<algorithm>
- #include<cstring>
- #include<cmath>
- #include<set>
- using namespace std;
- #define sqr(x) ((x)*(x))
- #define dsi(n) int n;scanf("%d",&n)
- #define si(n) scanf("%d",&n)
- #define f(i,n) for(int i=1;i<=n;++i)
- #define fi(n) f(i,n)
- #define f0(i,n) for(int i=0;i!=n;++i)
- #define fd(i,n) for(int i=n;i>=1;--i)
- #define ci const int&
- #define foreach(i,s) for(typeof(s.begin()) i=s.begin();i!=s.end();++i)
- string s[1000]={};
- int main()
- {
- char c1=0,c2=0;
- dsi(n);
- fi(n)cin>>s[i];
- fi(n)f(j,n)
- if(i==j||i+j-1==n){
- if(c1&&s[i][j-1]!=c1)
- {
- cout<<"NO";return 0;
- }
- if(!c1)c1=s[i][j-1];
- }else{
- if(c2&&s[i][j-1]!=c2)
- {
- cout<<"NO";return 0;
- }
- if(!c2)c2=s[i][j-1];
- }
- if(c1==c2)//fixed:全同色情况//
- {
- cout<<"NO";return 0;
-
- }
- cout<<"YES";return 0;
- }