面试题：Objective-C迭代器模式在复杂框架中的优化

1. 内存占用优化

复用迭代器对象：避免每次遍历都创建新的迭代器实例。可以使用对象池来管理迭代器对象，在需要时从对象池中获取，使用完毕后归还到对象池中。
减少数据拷贝：迭代器在遍历数据结构时，尽量避免对数据进行不必要的拷贝。如果数据结构中的元素较大，应该传递引用而不是值。

2. 遍历效率优化

使用高效的数据结构：根据实际需求选择合适的数据结构。例如，对于频繁插入和删除操作的场景，链表可能更合适；对于随机访问频繁的场景，数组可能更高效。
采用分块遍历：对于非常大的数据结构，可以将其分成多个小块，每次只遍历一个小块，这样可以减少一次性加载的数据量，提高遍历效率。

代码示例

// 定义一个协议表示可遍历的对象
@protocol Traversable <NSObject>
- (id<Iterator>)createIterator;
@end

// 定义一个协议表示迭代器
@protocol Iterator <NSObject>
- (BOOL)hasNext;
- (id)next;
@end

// 具体的数据结构类，实现Traversable协议
@interface MyDataStructure : NSObject <Traversable>
@property (nonatomic, strong) NSMutableArray *data;

- (instancetype)initWithData:(NSArray *)data;
@end

@implementation MyDataStructure
- (instancetype)initWithData:(NSArray *)data {
    self = [super init];
    if (self) {
        _data = [NSMutableArray arrayWithArray:data];
    }
    return self;
}

- (id<Iterator>)createIterator {
    return [[MyIterator alloc] initWithData:self.data];
}
@end

// 具体的迭代器类，实现Iterator协议
@interface MyIterator : NSObject <Iterator>
@property (nonatomic, strong) NSMutableArray *data;
@property (nonatomic, assign) NSUInteger currentIndex;

- (instancetype)initWithData:(NSMutableArray *)data;
@end

@implementation MyIterator
- (instancetype)initWithData:(NSMutableArray *)data {
    self = [super init];
    if (self) {
        _data = data;
        _currentIndex = 0;
    }
    return self;
}

- (BOOL)hasNext {
    return self.currentIndex < self.data.count;
}

- (id)next {
    if ([self hasNext]) {
        id object = self.data[self.currentIndex];
        self.currentIndex++;
        return object;
    }
    return nil;
}
@end

// 使用示例
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSArray *dataArray = @[@"A", @"B", @"C", @"D"];
        MyDataStructure *dataStructure = [[MyDataStructure alloc] initWithData:dataArray];
        id<Iterator> iterator = [dataStructure createIterator];
        while ([iterator hasNext]) {
            id object = [iterator next];
            NSLog(@"%@", object);
        }
    }
    return 0;
}

优化策略代码示例

复用迭代器对象（对象池示例）

// 迭代器对象池类
@interface IteratorPool : NSObject
@property (nonatomic, strong) NSMutableArray<MyIterator *> *pool;

+ (instancetype)sharedPool;
- (MyIterator *)getIteratorWithData:(NSMutableArray *)data;
- (void)returnIterator:(MyIterator *)iterator;
@end

@implementation IteratorPool
+ (instancetype)sharedPool {
    static IteratorPool *sharedPool = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedPool = [[IteratorPool alloc] init];
        sharedPool.pool = [NSMutableArray array];
    });
    return sharedPool;
}

- (MyIterator *)getIteratorWithData:(NSMutableArray *)data {
    if (self.pool.count > 0) {
        MyIterator *iterator = self.pool.lastObject;
        [self.pool removeLastObject];
        iterator.data = data;
        iterator.currentIndex = 0;
        return iterator;
    }
    return [[MyIterator alloc] initWithData:data];
}

- (void)returnIterator:(MyIterator *)iterator {
    iterator.data = nil;
    iterator.currentIndex = 0;
    [self.pool addObject:iterator];
}
@end

// 修改后的使用示例
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSArray *dataArray = @[@"A", @"B", @"C", @"D"];
        MyDataStructure *dataStructure = [[MyDataStructure alloc] initWithData:dataArray];
        IteratorPool *pool = [IteratorPool sharedPool];
        MyIterator *iterator = [pool getIteratorWithData:dataStructure.data];
        while ([iterator hasNext]) {
            id object = [iterator next];
            NSLog(@"%@", object);
        }
        [pool returnIterator:iterator];
    }
    return 0;
}

分块遍历示例

// 修改MyDataStructure类支持分块遍历
@interface MyDataStructure : NSObject <Traversable>
@property (nonatomic, strong) NSMutableArray *data;
@property (nonatomic, assign) NSUInteger chunkSize;

- (instancetype)initWithData:(NSArray *)data chunkSize:(NSUInteger)chunkSize;
@end

@implementation MyDataStructure
- (instancetype)initWithData:(NSArray *)data chunkSize:(NSUInteger)chunkSize {
    self = [super init];
    if (self) {
        _data = [NSMutableArray arrayWithArray:data];
        _chunkSize = chunkSize;
    }
    return self;
}

- (id<Iterator>)createIterator {
    return [[MyChunkIterator alloc] initWithData:self.data chunkSize:self.chunkSize];
}
@end

// 分块迭代器类
@interface MyChunkIterator : NSObject <Iterator>
@property (nonatomic, strong) NSMutableArray *data;
@property (nonatomic, assign) NSUInteger chunkSize;
@property (nonatomic, assign) NSUInteger currentIndex;
@property (nonatomic, assign) NSUInteger currentChunkIndex;

- (instancetype)initWithData:(NSMutableArray *)data chunkSize:(NSUInteger)chunkSize;
@end

@implementation MyChunkIterator
- (instancetype)initWithData:(NSMutableArray *)data chunkSize:(NSUInteger)chunkSize {
    self = [super init];
    if (self) {
        _data = data;
        _chunkSize = chunkSize;
        _currentIndex = 0;
        _currentChunkIndex = 0;
    }
    return self;
}

- (BOOL)hasNext {
    return self.currentIndex < self.data.count;
}

- (id)next {
    if (![self hasNext]) {
        return nil;
    }
    NSUInteger endIndex = MIN(self.currentIndex + self.chunkSize, self.data.count);
    NSArray *chunk = [self.data subarrayWithRange:NSMakeRange(self.currentIndex, endIndex - self.currentIndex)];
    self.currentIndex = endIndex;
    self.currentChunkIndex++;
    return chunk;
}
@end

// 使用分块遍历示例
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSArray *dataArray = @[@"A", @"B", @"C", @"D", @"E", @"F", @"G", @"H"];
        MyDataStructure *dataStructure = [[MyDataStructure alloc] initWithData:dataArray chunkSize:3];
        id<Iterator> iterator = [dataStructure createIterator];
        while ([iterator hasNext]) {
            NSArray *chunk = [iterator next];
            NSLog(@"Chunk %lu: %@", (unsigned long)self.currentChunkIndex, chunk);
        }
    }
    return 0;
}

星途面试题库

面试题：Objective-C迭代器模式在复杂框架中的优化

知识考点

面试题答案

1. 内存占用优化

2. 遍历效率优化

代码示例

优化策略代码示例

复用迭代器对象（对象池示例）

分块遍历示例