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

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 #import <foundation/foundation.h> @interface bbsinglelinkednode : nsobject <nscopying> @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

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 #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

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 #import <foundation/foundation.h> @interface bblinkednode : nsobject <nscopying> @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

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 #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)isnodeexist