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具体代码 : https://github.com/coderMyy/MYDictionary
OC中的字典实际上为一个数组 , 数组中的每个元素同样为一个链表实现的数组 ,也就是数组中套数组。
为什么要这么设计 ?
原因有二:
1. 每个对象创建时,都默认生成一个hashCode ,也就是一个经过哈希算法生成的一串数字 。当利用key去取字典中的value时,若是使用遍历或者二分查找等方法,效率都相对较低 ,于是出现了根据每个key生成的hashCode将该键值对放到hashCode对应的数组中的指定位置,这样当用key去取值时,便不必遍历去获取,即可以根据hashCode直接取出。
2. hashCode数字过大,或许会经过取余生成一个较小的数字,假如是对999取余,那么得到的结果始终处于0-999之间。但是,这样做的弊端在于取余所得到的值,可能是相同的,这样可能导致完全不相干的键值对被新的键值对(取余后值key相等)所覆盖。于是出现了数组中套链表实现的数组。这样,key值取余得到值相等的键值对,都将保存在同一个链表数组中,当查找key对应的值时,首先获取到该链表数组,然后遍历该数组,取正确的key所对应的值即可。
具体代码如下:
链表实现的数组
#import <Foundation/Foundation.h>
@interface MYLinkedArray : NSObject
@property (assign , nonatomic) NSUInteger size; //数组长度
- (void)addObject:(NSObject *)obj; //添加元素
- (void)remove:(NSObject *)obj; //移除指定元素
- (void)removeAtIndex:(NSInteger)index; //移除指定索引元素
- (NSObject *)objectAtIndex:(NSInteger)index; //获取指定位置的值
+ (instancetype)array; //数组初始化
@end
@interface Node : NSObject
@property (strong , nonatomic) Node *previous; //上个节点
@property (strong , nonatomic) Node *next; //下个节点
@property (strong , nonatomic) id content; //当前节点内容
@end
. m文件
#import "MYLinkedArray.h"
@interface MYLinkedArray ()
@property (nonatomic, strong) Node *first; //首个节点
@property (nonatomic, strong) Node *last; //最后节点
@end
@implementation MYLinkedArray
//添加元素
- (void)addObject:(NSObject *)obj
{
if (!obj) return;
_size ++ ;
Node *node = [[Node alloc]init];
//首个节点为空
if (!_first) {
_first = node;
_last = node;
node.previous = nil;
node.next = nil;
node.content = obj;
return;
}
//数组中有值
node.previous = _last;
node.next = nil;
node.content = obj;
_last = node;
_last.next = node;
}
//移除元素
- (void)remove:(NSObject *)obj
{
if (!obj||!_size) return;
Node *tmpNode = _first;
for (NSInteger index = 0; index < _size; index ++) {
if ([tmpNode.content isEqual:obj]) {
[self removeNode:tmpNode]; //移除节点
break;
}
}
}
//根据索引移除元素
- (void)removeAtIndex:(NSInteger)index
{
if (index<0||index>=_size) return;
Node *tmpNode = _first;
for (NSInteger i = 0; i < _size; i ++) {
if (i == index) {
[self removeNode:tmpNode]; //移除节点
break;
}
tmpNode = tmpNode.next;
}
}
//获取指定索引元素
- (NSObject *)objectAtIndex:(NSInteger)index
{
if (index<0||index>=_size) return nil;
Node *tmpNode = _first;
for (NSInteger i = 0; i < _size; i ++) {
if (i == index) {
return tmpNode.content;
}
tmpNode = tmpNode.next;
}
return nil;
}
//私有
- (void)removeNode:(Node *)node
{
//连接上下节点
Node *preNode = node.previous;
Node *nextNode = node.next;
preNode.next = nextNode;
nextNode.previous = preNode;
node.content = nil; //清空被移除节点内容
_size -- ;//长度更新
}
//构造方法
+ (instancetype)array
{
return [[self alloc]init];
}
@end
@implementation Node
@end
自定义的字典类
#import <Foundation/Foundation.h>
@interface MYDictionary : NSObject
+ (instancetype)dictionary;
- (void)setValue:(id)value forkey:(NSString *)key;
- (id)valueForKey:(NSString *)key;
@end
. m文件
#import "MYDictionary.h"
#import "MYLinkedArray.h"
@interface KeyValueCache : NSObject
@property (nonatomic, strong) NSString *key;
@property (nonatomic, strong) id value;
@end
@implementation KeyValueCache
+ (instancetype)key:(NSString *)key value:(id)value
{
KeyValueCache *model = [[self alloc]init];
model.key = key;
model.value = value;
return model;
}
@end
@interface MYDictionary ()
@end
@implementation MYDictionary
{
MYLinkedArray *_keyValues[999];
}
//构造方法
+ (instancetype)dictionary
{
return [[self alloc]init];
}
//赋值
- (void)setValue:(id)value forkey:(NSString *)key
{
//获取hashCode
NSUInteger hash = key.hash;
//默认一个对象占用8个字节
NSUInteger realCode = hash%(sizeof(_keyValues)/8);
MYLinkedArray *linkArr = _keyValues[realCode];
if (linkArr) { //如果存在链表数组
for (NSInteger index = 0; index < linkArr.size; index ++) {
KeyValueCache *keyValue = (KeyValueCache *)[linkArr objectAtIndex:index];
if ([keyValue.key isEqualToString:key]) { //如果存在相同的Key ,更新value
keyValue.value = value; //重新赋值value
return;
}
}
//创建新的键值对存储
KeyValueCache *newKeyValue = [KeyValueCache key:key value:value];
[linkArr addObject:newKeyValue];
}else{ //不存在链表数组
//创建新的链表数组
MYLinkedArray *newLinkArray = [MYLinkedArray array];
KeyValueCache *newKeyValue = [KeyValueCache key:key value:value];
[newLinkArray addObject:newKeyValue];
_keyValues[realCode] = newLinkArray;
}
}
//根据键取值
- (id)valueForKey:(NSString *)key
{
if (!key.length) return nil;
//获取hashCode
NSUInteger hash = key.hash;
NSUInteger realCode = hash%(sizeof(_keyValues)/8);
MYLinkedArray *linkArr = _keyValues[realCode];
if (linkArr) {
//遍历链表,取出value
for (NSInteger index = 0; index < linkArr.size; index ++) {
KeyValueCache *keyvalue = (KeyValueCache *)[linkArr objectAtIndex:index];
if ([keyvalue.key isEqualToString:key]) {
return keyvalue.value;
}
}
}
return nil;
}
@end
最终实验结果:
- (void)viewDidLoad {
[super viewDidLoad];
MYDictionary *dict = [MYDictionary dictionary];
[dict setValue:@"哈哈" forkey:@"孟"];
[dict setValue:@"你好" forkey:@"孟"];
[dict setValue:@123456 forkey:@"数字"];
NSLog(@"%@",[dict valueForKey:@"孟"]);
NSLog(@"%@",[dict valueForKey:@"数字"]);
}
成功自定义了一个字典.