BOOL checkDuplicates(NSString *str)
{
NSMutableArray *storageArray = [NSMutableArray array];
for (int i = 0; i < str.length; i++) {
NSString *charStr = [str substringWithRange:NSMakeRange(i,1)];
if ([storageArray containsObject: charStr]) {
return true;
} else {
[storageArray addObject: charStr];
}
}
return false;
}