通过分类为数组添加一个倒序的一个方法. 比如: 数组中元素为 @”aa”, @”bb”, @”cc”, @”dd”, @”ee”, 倒序完之后为: @”ee”, @”dd”,@”cc”,@”bb”,@

@interface NSArray (BackOfNSArray)
//1.	通过分类为数组添加一个倒序的一个方法. 比如: 数组中元素为 @”aa”, @”bb”, @”cc”, @”dd”, @”ee”, 倒序完之后为: @”ee”, @”dd”,@”cc”,@”bb”,@”aa”.
- (void)back:(NSMutableArray *)aArray;
@end
#import "NSArray+BackOfNSArray.h"

@implementation NSArray (BackOfNSArray)
- (void)back:(NSMutableArray *)aArray {
NSUInteger count = [aArray count];
for (NSUInteger i = 0; i < count / 2; i++) {
[aArray exchangeObjectAtIndex:i withObjectAtIndex:count - 1 - i];
}
}
@end
NSMutableArray *arr = [NSMutableArray arrayWithObjects:@"aa", @"bb", @"cc", @"dd", @"ee", nil];
[arr back:arr];
NSLog(@"%@", arr);