iOS 数据结构之数组的操作方法

数组是线性结构是容器类型,是一块连续的内存空间, ios 中用 nsarray 和 nsmutablearray 集合类型,用来存放对象类型,其中 nsarray是不可变类型, nsmutablearray 是可变类型,能够对数组中元素进行增删改查.

本文作者本着学习的态度,决定仿照nsarray和nsmutablearray 自己实现一个数组类型,当然性能可能没有 nsarray和nsmutablearray 的好,插入100000万条数据,时间上是 nsmutablearray 的三倍左右 ,当然平时使用过程中很少100000次这样大的数据往数组里添加,因此性能方面可以忽略.

arraylist.h 主要方法声明 完全照搬 nsarray 和 nsmutablearray 的方法名称

先发下测试结果

dispatch_async(dispatch_get_global_queue(0, 0), ^{
    person *p1 = [[person alloc] init];
    nsmutablearray *array = [nsmutablearray arraywithcapacity:100000];
//   arraylist
  *array = [arraylist arraywithcapacity:100000];
    cfabsolutetime starttime =cfabsolutetimegetcurrent();
    for (int i = 0; i<100000; i++) {
      [array addobject:p1];
    }
    cfabsolutetime linktime = (cfabsolutetimegetcurrent() - starttime);
    cftimeinterval duration = linktime * 1000.0f;
    nslog(@"linked in %f ms",duration);
    [self->_timearray addobject:@(duration)];
    count++;
  });
nsmutablearray 5.081740292635832 ms
arraylist 16.27591523257168 ms
以下是 arraylist 的具体实现 ,内部是一个 c语言的数组用来存放对象
//
// arraylist.m
// arraylist
//
// created by dzb on 2018/7/19.
// copyright © 2018 大兵布莱恩特. all rights reserved.
//
#import "arraylist.h"
static nsinteger const defaultcapacity = 10;
typedef void * anyobject;
@interface arraylist ()
{
  anyobject *_array;
  nsinteger _size;
  nsinteger _capacity;
}
@end
@implementation arraylist
#pragma mark - init
- (instancetype)init
{
  self = [super init];
  if (self) {
    [self resetarray];
  }
  return self;
}
+ (instancetype)array {
  return [[arraylist alloc] initwithcapacity:defaultcapacity];
}
+ (instancetype)arraywithcapacity:(nsuinteger)numitems {
  return [[arraylist alloc] initwithcapacity:numitems];
}
- (instancetype)initwithcapacity:(nsuinteger)numitems {
  _capacity = numitems;
  _array = calloc(_capacity,sizeof(anyobject));
  _size = 0;
  return self;
}
/**
 数组重置
 */
- (void) resetarray {
  _size = 0;
  if (_array != null)
    _array[_size] = null;
    free(_array);
  _capacity = defaultcapacity;
  _array = calloc(_capacity, sizeof(anyobject));
}
#pragma makr - 增加操作
- (void)addobject:(id)anobject {
  [self insertobject:anobject atindex:_size];
}
- (void)insertobject:(id)anobject atindex:(nsuinteger)index {
  if (!anobject) {
    @throw [nsexception exceptionwithname:@"add object null." reason:@"object must be not null ." userinfo:nil];
    return;
  }
  ///判越界
  if ((index > _size)) {
    @throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
    return;
  }
  if (_size == _capacity-1) { ///判断原来数组是否已经满了 如果满了就需要增加数组长度
    [self resize:2*_capacity];
  }
  ///交换索引位置
  if (self.count > 0 ) {
    for(nsinteger i = _size - 1 ; i >= index ; i--)
      _array[i + 1] = _array[i];
  }
  self->_array[index] = (__bridge_retained anyobject)(anobject);
  _size++;
}
#pragma mark - 删除操作
- (void)removeallobjects {
  nsinteger i = _size-1;
  while (_size > 0) {
    [self removeobjectatindex:i];
    i--;
  }
  [self resetarray];
}
- (void)removeobjectatindex:(nsuinteger)index {
  ///判断越界
  if ((index > _size)) {
    @throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
    return;
  }
  anyobject object =(_array[index]);
  cfrelease(object);
  for(nsinteger i = index + 1 ; i < _size ; i ++)
    _array[i - 1] = _array[i];
  _size--;
  _array[_size] = null;
  ///对数组空间缩减
  if (_size == _capacity/2) {
    [self resize:_capacity/2];
  }
}
- (void)removeobject:(id)anobject {
  nsinteger index = [self indexofobject:anobject];
  if (index == nsnotfound) return;
  [self removeobjectatindex:index];
}
- (void)removelastobject {
  if ([self isempty]) return;
  [self removeobjectatindex:_size-1];
}
#pragma mark - 修改操作
- (void)replaceobjectatindex:(nsuinteger)index withobject:(id)anobject {
  if (!anobject) {
    @throw [nsexception exceptionwithname:@"add object null." reason:@"object must be not null ." userinfo:nil];
    return;
  }
  ///判断越界
  if ((index > _size)) {
    @throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
    return;
  }
  _array[index] = (__bridge anyobject)(anobject);
}
#pragma mark - 查询操作
- (bool) isempty {
  return (self->_size == 0);
}
- (bool) isfull {
  return (self->_size == self->_capacity-1);
}
- (id)objectatindex:(nsuinteger)index {
  if ((index > _size)) {
    @throw [nsexception exceptionwithname:@"array is out of bounds" reason:@"out of bounds" userinfo:nil];
    return nil;
  }
  if ([self isempty]) { return nil; }
  anyobject obj = _array[index];
  if (obj == null) return nil;
  return (__bridge id)(obj);
}
- (nsuinteger)indexofobject:(id)anobject {
  for (int i = 0; i<_size; i++) {
    id obj = (__bridge id)(_array[i]);
    if ([anobject isequal:obj]) return i;
  }
  return nsnotfound;
}
- (bool)containsobject:(id)anobject {
  for (int i = 0; i<_size; i++) {
    id obj = (__bridge id)(_array[i]);
    if ([anobject isequal:obj]) return yes;
  }
  return no;
}
- (id)firstobject {
  if ([self isempty]) return nil;
  return (__bridge id _nullable)(_array[0]);
}
- (id)lastobject {
  if ([self isempty]) return nil;
  return (__bridge id _nullable)(_array[_size]);
}
- (nsuinteger)count {
  return _size;
}
- (nsstring *)description {
  nsmutablestring *string = [nsmutablestring stringwithformat:@"\narraylist %p : [ \n" ,self];
  for (int i = 0; i<_size; i++) {
    anyobject obj = _array[i];
    [string appendformat:@"%@",(__bridge id)obj];
    if (i<_size-1) {
      [string appendstring:@" , \n"];
    }
  }
  [string appendstring:@"\n]\n"];
  return string;
}
/**
 对数组扩容
 @param capacity 新的容量
 */
- (void) resize:(nsinteger)capacity {
  anyobject *oldarray = _array;
  anyobject *newarray = calloc(capacity, sizeof(anyobject));
  for (int i = 0 ; i<_size; i++) {
    newarray[i] = oldarray[i];
  }
  _array = newarray;
  _capacity = capacity;
  free(oldarray);
}
- (void)dealloc
{
  if (_array != null)
    [self removeallobjects];
  free(_array);
// nslog(@"arraylist dealloc");
}
@end

经过测试 数组内部会对存入的对象 进行 retain 操作 其引用计数+1 ,当对象从数组中移除的时候 能够正常的使对象内存引用计数-1,因此不必担心对象内存管理的问题. 数组默认长度是10 , 如果在开发者不确定数组长度时候 ,其内部可以动态的扩容增加数组长度,当执行 remove 操作时候 也会对数组内部长度 进行相应的缩减

实现了 nsarray 和 nsmutablearray 等常用api,如果不是对性能特别在意的场景下 ,可以使用 arraylist 来存放一些数据

原文链接：http://www.cocoachina.com/ios/20180723/24275.html