题目地址：传送门
Description
You are given string s. Your task is to determine if the given string s contains two non-overlapping substrings "AB" and "BA" (the substrings can go in any order).
Input
The only line of input contains a string s of length between 1 and 105 consisting of uppercase Latin letters.
Output
Print "YES" (without the quotes), if string s contains two non-overlapping substrings "AB" and "BA", and "NO" otherwise.
Sample Input
ABA
NO
BACFAB
YES
AXBYBXA
NO
Hint
In the first sample test, despite the fact that there are substrings "AB" and "BA", their occurrences overlap, so the answer is "NO".
In the second sample test there are the following occurrences of the substrings: BACFAB.
In the third sample test there is no substring "AB" nor substring "BA".
题解：这里可以使用strstr()函数，需要<string.h>头文件
#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
char s[100001];
int main(){
char *c;
scanf("%s",&s);
if((c=strstr(s,"AB"))!=NULL&&strstr(c+2,"BA")!=NULL){
printf("YES\n");
return 0;
}
if((c=strstr(s,"BA"))!=NULL&&strstr(c+2,"AB")!=NULL){
printf("YES\n");
return 0;
}
printf("NO\n");
}
原文：http://blog.csdn.net/qq_26891045/article/details/52218488