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);