所以答案最多有3位,暴力就可以
#include<cstdio> #include<cstring> #include<cstdlib> #include<algorithm> #include<functional> #include<iostream> #include<cmath> #include<cctype> #include<ctime> using namespace std; #define For(i,n) for(int i=1;i<=n;i++) #define Fork(i,k,n) for(int i=k;i<=n;i++) #define Rep(i,n) for(int i=0;i<n;i++) #define ForD(i,n) for(int i=n;i;i--) #define RepD(i,n) for(int i=n;i>=0;i--) #define Forp(x) for(int p=pre[x];p;p=next[p]) #define Forpiter(x) for(int &p=iter[x];p;p=next[p]) #define Lson (x<<1) #define Rson ((x<<1)+1) #define MEM(a) memset(a,0,sizeof(a)); #define MEMI(a) memset(a,127,sizeof(a)); #define MEMi(a) memset(a,128,sizeof(a)); #define INF (2139062143) #define F (100000007) #define MAXN (100000+10) typedef long long ll; ll mul(ll a,ll b){return (a*b)%F;} ll add(ll a,ll b){return (a+b)%F;} ll sub(ll a,ll b){return (a-b+(a-b)/F*F+F)%F;} void upd(ll &a,ll b){a=(a%F+b%F)%F;} char s[MAXN]; int main() { // freopen("I.in","r",stdin); // freopen(".out","w",stdout); scanf("%s",s); char *pch=strstr(s,"AB"); if (pch!=NULL&&strstr(pch+2,"BA")!=NULL) { cout<<"YES"<<endl; return 0; } pch=strstr(s,"BA"); if (pch!=NULL&&strstr(pch+2,"AB")!=NULL) { cout<<"YES"<<endl; return 0; } cout<<"NO"<<endl; return 0; }