链表（Linked List）是一种物理存储单元上非连续、非顺序的存储结构，数据元素的逻辑顺序是通过链表中的指针链接次序实现的，表现形式如下图所示：
单链表
双链表
数组和链表区别：
数组：数组元素在内存上连续存放，可以通过下标查找元素；插入、删除需要移动大量元素，比较适用于元素很少变化的情况
链表：链表中的元素在内存中不是顺序存储的，查找慢，插入、删除只需要对元素指针重新赋值，效率高
Objective-C 里没有现成的链表结构，下面我实现了非线程安全的单链表和双链表，以下都是具体的实现细节，完整代码可以在这儿下载
单链表
单链表提供了插入、删除、查询、反转等操作，具体实现如下：
BBSingleLinkedList.h
#import
@interface BBSingleLinkedNode : NSObject
@property (nonatomic, strong) NSString *key;
@property (nonatomic, strong) NSString *value;
@property (nonatomic, strong) BBSingleLinkedNode *next;
- (instancetype)initWithKey:(NSString *)key
value:(NSString *)value;
+ (instancetype)nodeWithKey:(NSString *)key
value:(NSString *)value;
@end
@interface BBSingleLinkedList : NSObject
- (void)insertNode:(BBSingleLinkedNode *)node;
- (void)insertNodeAtHead:(BBSingleLinkedNode *)node;
- (void)insertNode:(BBSingleLinkedNode *)newNode beforeNodeForKey:(NSString *)key;
- (void)insertNode:(BBSingleLinkedNode *)newNode afterNodeForKey:(NSString *)key;
- (void)bringNodeToHead:(BBSingleLinkedNode *)node;
- (void)removeNode:(BBSingleLinkedNode *)node;
- (BBSingleLinkedNode *)nodeForKey:(NSString *)key;
- (BBSingleLinkedNode *)headNode;
- (BBSingleLinkedNode *)lastNode;
- (NSInteger)length;
- (BOOL)isEmpty;
- (void)reverse;
- (void)readAllNode;
@end
BBSingleLinkedList.m
#import "BBSingleLinkedList.h"
@implementation BBSingleLinkedNode
- (instancetype)initWithKey:(NSString *)key
value:(NSString *)value
{
if (self = [super init]) {
_key = key;
_value = value;
}
return self;
}
+ (instancetype)nodeWithKey:(NSString *)key
value:(NSString *)value
{
return [[[self class] alloc] initWithKey:key value:value];
}
#pragma mark - NSCopying
- (id)copyWithZone:(nullable NSZone *)zone
{
BBSingleLinkedNode *newNode = [[BBSingleLinkedNode allocWithZone:zone] init];
newNode.key = self.key;
newNode.value = self.value;
newNode.next = self.next;
return newNode;
}
@end
@interface BBSingleLinkedList ()
@property (nonatomic, strong) BBSingleLinkedNode *headNode;
@property (nonatomic, strong) NSMutableDictionary *innerMap;
@end
@implementation BBSingleLinkedList
- (instancetype)init
{
self = [super init];
if (self) {
_innerMap = [NSMutableDictionary new];
}
return self;
}
#pragma mark - public
- (void)insertNodeAtHead:(BBSingleLinkedNode *)node
{
if (!node || node.key.length == 0) {
return;
}
if ([self isNodeExists:node]) {
return;
}
_innerMap[node.key] = node;
if (_headNode) {
node.next = _headNode;
_headNode = node;
} else {
_headNode = node;
}
}
- (void)insertNode:(BBSingleLinkedNode *)node
{
if (!node || node.key.length == 0) {
return;
}
if ([self isNodeExists:node]) {
return;
}
_innerMap[node.key] = node;
if (!_headNode) {
_headNode = node;
return;
}
BBSingleLinkedNode *lastNode = [self lastNode];
lastNode.next = node;
}
- (void)insertNode:(BBSingleLinkedNode *)newNode beforeNodeForKey:(NSString *)key
{
if (key.length == 0 || !newNode || newNode.key.length == 0) {
return;
}
if ([self isNodeExists:newNode]) {
return;
}
if (!_headNode) {
_headNode = newNode;
return;
}
BBSingleLinkedNode *node = _innerMap[key];
if (node) {
_innerMap[newNode.key] = newNode;
BBSingleLinkedNode *aheadNode = [self nodeBeforeNode:node];
if (aheadNode) {
aheadNode.next = newNode;
newNode.next = node;
} else {
_headNode = newNode;
newNode.next = node;
}
} else {
[self insertNode:newNode]; //insert to tail
}
}
- (void)insertNode:(BBSingleLinkedNode *)newNode afterNodeForKey:(NSString *)key
{
if (key.length == 0 || !newNode || newNode.key.length == 0) {
return;
}
if ([self isNodeExists:newNode]) {
return;
}
if (!_headNode) {
_headNode = newNode;
return;
}
BBSingleLinkedNode *node = _innerMap[key];
if (node) {
_innerMap[newNode.key] = newNode;
newNode.next = node.next;
node.next = newNode;
} else {
[self insertNode:newNode]; //insert to tail
}
}
- (void)removeNode:(BBSingleLinkedNode *)node
{
if (!node || node.key.length == 0) {
return;
}
[_innerMap removeObjectForKey:node.key];
if (node.next) {
node.key = node.next.key;
node.value = node.next.value;
node.next = node.next.next;
} else {
BBSingleLinkedNode *aheadNode = [self nodeBeforeNode:node];
aheadNode.next = nil;
}
}
- (void)bringNodeToHead:(BBSingleLinkedNode *)node
{
if (!node || !_headNode) {
return;
}
if ([node isEqual:_headNode]) {
return;
}
BBSingleLinkedNode *aheadNode = [self nodeBeforeNode:node];
aheadNode.next = node.next;
node.next = _headNode;
_headNode = node;
}
- (BBSingleLinkedNode *)nodeForKey:(NSString *)key
{
if (key.length == 0) {
return nil;
}
BBSingleLinkedNode *node = _innerMap[key];
return node;
}
- (BBSingleLinkedNode *)headNode
{
return _headNode;
}
- (BBSingleLinkedNode *)lastNode
{
BBSingleLinkedNode *last = _headNode;
while (last.next) {
last = last.next;
}
return last;
}
- (void)reverse
{
BBSingleLinkedNode *prev = nil;
BBSingleLinkedNode *current = _headNode;
BBSingleLinkedNode *next = nil;
while (current) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
_headNode = prev;
}
- (void)readAllNode
{
BBSingleLinkedNode *tmpNode = _headNode;
while (tmpNode) {
NSLog(@"node key -- %@, node value -- %@", tmpNode.key, tmpNode.value);
tmpNode = tmpNode.next;
}
}
- (NSInteger)length
{
NSInteger _len = 0;
for (BBSingleLinkedNode *node = _headNode; node; node = node.next) {
_len ++;
}
return _len;
}
- (BOOL)isEmpty
{
return _headNode == nil;
}
#pragma mark - private
- (BBSingleLinkedNode *)nodeBeforeNode:(BBSingleLinkedNode *)node
{
BBSingleLinkedNode *targetNode = nil;
BBSingleLinkedNode *tmpNode = _headNode;
while (tmpNode) {
if ([tmpNode.next isEqual:node]) {
targetNode = tmpNode;
break;
} else {
tmpNode = tmpNode.next;
}
}
return targetNode;
}
- (BOOL)isNodeExists:(BBSingleLinkedNode *)node
{
BBSingleLinkedNode *tmpNode = _headNode;
while (tmpNode) {
if ([tmpNode isEqual:node]) {
return YES;
}
tmpNode = tmpNode.next;
}
return false;
}
@end
双链表
双链表提供了插入、删除、查询操作，具体实现如下：
BBLinkedMap.h
#import
@interface BBLinkedNode : NSObject
@property (nonatomic, strong) NSString *key;
@property (nonatomic, strong) NSString *value;
@property (nonatomic, strong) BBLinkedNode *prev;
@property (nonatomic, strong) BBLinkedNode *next;
- (instancetype)initWithKey:(NSString *)key
value:(NSString *)value;
+ (instancetype)nodeWithKey:(NSString *)key
value:(NSString *)value;
@end
@interface BBLinkedMap : NSObject
- (void)insertNodeAtHead:(BBLinkedNode *)node;
- (void)insertNode:(BBLinkedNode *)node;
- (void)insertNode:(BBLinkedNode *)newNode beforeNodeForKey:(NSString *)key;
- (void)insertNode:(BBLinkedNode *)newNode afterNodeForKey:(NSString *)key;
- (void)bringNodeToHead:(BBLinkedNode *)node;
- (void)readAllNode;
- (void)removeNodeForKey:(NSString *)key;
- (void)removeTailNode;
- (NSInteger)length;
- (BOOL)isEmpty;
- (BBLinkedNode *)nodeForKey:(NSString *)key;
- (BBLinkedNode *)headNode;
- (BBLinkedNode *)tailNode;
@end
BBLinkedMap.m
#import "BBLinkedMap.h"
@implementation BBLinkedNode
- (instancetype)initWithKey:(NSString *)key
value:(NSString *)value
{
if (self = [super init]) {
_key = key;
_value = value;
}
return self;
}
+ (instancetype)nodeWithKey:(NSString *)key
value:(NSString *)value
{
return [[[self class] alloc] initWithKey:key value:value];
}
#pragma mark - NSCopying
- (id)copyWithZone:(nullable NSZone *)zone
{
BBLinkedNode *newNode = [[BBLinkedNode allocWithZone:zone] init];
newNode.key = self.key;
newNode.value = self.value;
newNode.prev = self.prev;
newNode.next = self.next;
return newNode;
}
@end
@interface BBLinkedMap ()
@property (nonatomic, strong) BBLinkedNode *headNode;
@property (nonatomic, strong) BBLinkedNode *tailNode;
@property (nonatomic, strong) NSMutableDictionary *innerMap;
@end
@implementation BBLinkedMap
- (instancetype)init
{
self = [super init];
if (self) {
_innerMap = [NSMutableDictionary new];
}
return self;
}
#pragma mark - public
- (void)insertNodeAtHead:(BBLinkedNode *)node
{
if (!node || node.key.length == 0) {
return;
}
if ([self isNodeExists:node]) {
return;
}
_innerMap[node.key] = node;
if (_headNode) {
node.next = _headNode;
_headNode.prev = node;
_headNode = node;
} else {
_headNode = _tailNode = node;
}
}
- (void)insertNode:(BBLinkedNode *)node
{
if (!node || node.key.length == 0) {
return;
}
if ([self isNodeExists:node]) {
return;
}
if (!_headNode && !_tailNode) {
_headNode = _tailNode = node;
return;
}
_innerMap[node.key] = node;
_tailNode.next = node;
node.prev = _tailNode;
_tailNode = node;
}
- (void)insertNode:(BBLinkedNode *)newNode beforeNodeForKey:(NSString *)key
{
if (key.length == 0 || !newNode || newNode.key.length == 0) {
return;
}
if ([self isNodeExists:newNode]) {
return;
}
if (!_headNode && !_tailNode) {
_headNode = _tailNode = newNode;
return;
}
BBLinkedNode *node = _innerMap[key];
if (node) {
_innerMap[newNode.key] = newNode;
if (node.prev) {
node.prev.next = newNode;
newNode.prev = node.prev;
} else {
_headNode = newNode;
}
node.prev = newNode;
newNode.next = node;
} else {
[self insertNode:newNode]; //insert to tail
}
}
- (void)insertNode:(BBLinkedNode *)newNode afterNodeForKey:(NSString *)key
{
if (key.length == 0 || !newNode || newNode.key.length == 0) {
return;
}
if ([self isNodeExists:newNode]) {
return;
}
if (!_headNode && !_tailNode) {
_headNode = _tailNode = newNode;
return;
}
BBLinkedNode *node = _innerMap[key];
if (node) {
_innerMap[newNode.key] = newNode;
if (node.next) {
newNode.next = node.next;
node.next.prev = newNode;
} else {
_tailNode = newNode;
}
newNode.prev = node;
node.next = newNode;
} else {
[self insertNode:newNode]; //insert to tail
}
}
- (void)bringNodeToHead:(BBLinkedNode *)node
{
if (!node) {
return;
}
if (!_headNode && !_tailNode) {
_headNode = _tailNode = node;
return;
}
if ([_headNode isEqual:node]) {
return;
}
if ([_tailNode isEqual:node]) {
_tailNode = node.prev;
_tailNode.next = nil;
} else {
node.prev.next = node.next;
node.next.prev = node.prev;
}
_headNode.prev = node;
node.next = _headNode;
node.prev = nil;
_headNode = node;
}
- (void)removeNodeForKey:(NSString *)key
{
if (key.length == 0) {
return;
}
BBLinkedNode *node = _innerMap[key];
if (!node) {
return;
}
[_innerMap removeObjectForKey:key];
if ([_headNode isEqual:node]) {
_headNode = node.next;
} else if ([_tailNode isEqual:node]) {
_tailNode = node.prev;
}
node.prev.next = node.next;
node.next.prev = node.prev;
}
- (void)removeTailNode
{
if (!_tailNode || _tailNode.key.length == 0) {
return;
}
[_innerMap removeObjectForKey:_tailNode.key];
if (_headNode == _tailNode) {
_headNode = _tailNode = nil;
return;
}
_tailNode = _tailNode.prev;
_tailNode.next = nil;
}
- (BBLinkedNode *)nodeForKey:(NSString *)key
{
if (key.length == 0) {
return nil;
}
BBLinkedNode *node = _innerMap[key];
return node;
}
- (BBLinkedNode *)headNode
{
return _headNode;
}
- (BBLinkedNode *)tailNode
{
return _tailNode;
}
- (void)readAllNode
{
BBLinkedNode *node = _headNode;
while (node) {
NSLog(@"node key -- %@, node value -- %@", node.key, node.value);
node = node.next;
}
}
- (NSInteger)length
{
NSInteger _len = 0;
for (BBLinkedNode *node = _headNode; node; node = node.next) {
_len ++;
}
return _len;
}
- (BOOL)isEmpty
{
return _headNode == nil;
}
#pragma mark - private
- (BOOL)isNodeExists:(BBLinkedNode *)node
{
BBLinkedNode *tmpNode = _headNode;
while (tmpNode) {
if ([tmpNode isEqual:node]) {
return YES;
}
tmpNode = tmpNode.next;
}
return false;
}
@end
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