javascript实现数据结构: 串的块链存储表示

和线性表的链式存储结构相类似,也可采用链式方式存储串值。由于串结构的特殊性--结构中的每个数据元素是一个字符,则用链表存储串值时,存在一个“结点大小”的问题,即每个结点可以存放一个字符,也可以存放多个字符。

下面是结点大小为4(即每个结点存放4个字符)的链表:

head --> (a) --> (b) --> (c) --> ... --> (i)

当结点大小大于1时,由于串长不一定是结点大小的整倍数,则链表中的最后一个结点不一定全被串值占满,此时通常补上“#”或其它非串值字符。

为了便于进行串的操作,当以链表存储串值时,除头指针外还可附设一个尾指针指示链表中的最后一个结点,并给出当前串的长度,称如此定义的串存储结构为块链结构。

由于一般情况下,对串进行操作时,只需要从头向尾顺序扫描即可,则对串值不必建立双向链表。设尾指针的目的是为了便于进行连接操作,但应注意连接时需处理第一个串尾的无效字符。

在链式存储方式中,结点大小的选择和顺序存储方式的格式选择一样都很重要,它直接影响到串处理的效率。如果串很长,这要求我们考虑串值的存储密度:

存储密度 = 串值所占的存储位 / 实际分配的存储位

 

串值的链式存储结构对某些串操作,如连接操作等有一定方便之处,但总的来说不如另外两种存储结构灵活,它占用存储量大且操作复杂。

 

结构图:

javascript实现数据结构: 串的块链存储表示

实现代码:

javascript实现数据结构: 串的块链存储表示
  1 function Chunk(chunkSize) {
  2         this.chunkSize = chunkSize || 4;
  3         this.ch = [];
  4         for (var i = 0; i < this.chunkSize; i++) {
  5             this.ch[i] = ‘#‘;
  6         }
  7         // type: Chunk
  8         this.next = null;
  9     }
 10 
 11     exports.LString = LString;
 12     function LString(chunkSize) {
 13         // type Chunk
 14         this.head = null;
 15         // type: chunk
 16         this.tail = null;
 17         // 串的当前长度
 18         this.length = 0;
 19         this.chunkSize = chunkSize || 4;
 20     }
 21 
 22     LString.prototype = {
 23         // 将字符串转换成LString类型
 24         strAssign: function (chars) {
 25             this.head = this.tail = new Chunk(this.chunkSize);
 26             this.length = chars.length;
 27 
 28             var current = this.head;
 29             for (var i = 0, len = chars.length; i < len; i++) {
 30                 current.ch[i % this.chunkSize] = chars[i];
 31                 if (i + 1 < len && (i + 1) % this.chunkSize === 0) {
 32                     current.next = new Chunk();
 33                     current = current.next;
 34                 }
 35             }
 36 
 37             this.tail = current;
 38         },
 39         // 字符串对比
 40         // TODO 是否去掉chunkSize的对比
 41         strCompare: function (tLString) {
 42             var current = this.head;
 43             var curT = tLString.head;
 44 
 45             if (this.length !== tLString.length) return false;
 46 
 47             while (current) {
 48                 for (var i = 0; i < this.chunkSize; i++) {
 49                     if (current.ch[i] !== curT.ch[i]) return false;
 50                 }
 51 
 52                 current = current.next;
 53                 curT = curT.next;
 54             }
 55 
 56             return true;
 57         },
 58         clearString: function () {
 59             this.head = this.tail = null;
 60             this.length = 0;
 61         },
 62         concat: function (tLSting) {
 63             if (!tLSting.length) return;
 64 
 65             var ret = new LString(this.chunkSize);
 66 
 67             if (this.head === null) {
 68                 copyString(ret, tLSting);
 69             } else {
 70                 ret.head = ret.tail = new Chunk(this.chunkSize);
 71                 copyString(ret, this);
 72 
 73                 var index = ret.tail.ch.indexOf(‘#‘);
 74                 if (index === -1) {
 75                     copyString(ret, tLSting);
 76                 } else {
 77                     copyString(ret, tLSting, ret.tail, tLSting.head, index);
 78                 }
 79             }
 80 
 81             return ret;
 82         },
 83         substring: function (pos, len) {
 84             pos = ~~pos || 0;
 85             len = ~~len || this.length;
 86             if (pos < 0 || pos > this.length - 1 || len < 0 || len > this.length - pos)
 87                 throw new Error(‘unexpected parameter‘);
 88 
 89             var sub = new LString(this.chunkSize);
 90             var current = findPosChunk(this, pos);
 91             var curS = sub.head = new Chunk(this.chunkSize);
 92             var i = 0;
 93             sub.length = len;
 94 
 95             outerloop: while (current) {
 96                 for (var j = 0, size = this.chunkSize; j < size; j++) {
 97                     if (i === len) {
 98                         break outerloop;
 99                     } else {
100                         curS.ch[j] = current.ch[(i + pos) % this.chunkSize];
101                         i++;
102                         if ((i + pos) % this.chunkSize === 0) {
103                             current = current.next;
104                         }
105                         if (i % this.chunkSize === 0 && (current.ch[i] || current.next)) {
106                             curS.next = new Chunk(this.chunkSize);
107                             curS = curS.next;
108                         }
109                     }
110                 }
111             }
112 
113             return sub;
114         },
115         toString: function () {
116             var current = this.head;
117 
118             if (current === null) return ‘‘;
119 
120             var str = ‘‘;
121             while (current) {
122                 for (var i = 0, len = this.chunkSize; i < len; i++) {
123                     var ch = current.ch[i];
124                     if (ch === ‘#‘) {
125                         return str;
126                     } else {
127                         str += current.ch[i];
128                     }
129                 }
130                 current = current.next;
131             }
132 
133             return str;
134         }
135     };
136 
137     function findPosChunk(lString, pos) {
138         var current = lString.head;
139         while (current) {
140             for (var i = 0, len = lString.chunkSize; i < len; i++) {
141                 if (pos-- === 0) return current;
142             }
143             current = current.next;
144         }
145     }
146 
147     function copyString(destination, target, curD, currT, offset) {
148         offset = offset || 0;
149         currT = currT || target.head;
150         curD = curD || destination.head;
151         var k = 0;
152 
153         while (currT) {
154             for (var i = 0, len = target.chunkSize; i < len; i++, k++) {
155                 var j = k % curD.chunkSize + offset;
156                 curD.ch[j % curD.chunkSize] = currT.ch[i];
157 
158                 if ((j + 1) % curD.chunkSize === 0 && (currT.ch[i + 1] || currT.next)) {
159                     curD.next = new Chunk(destination.chunkSize);
160                     curD = curD.next;
161                 }
162             }
163 
164             currT = currT.next;
165         }
166 
167         destination.tail = curD;
168         destination.length += target.length;
169     }
170 
171     var a = new LString();
172     var b = new LString();
173     var c = new LString();
174 
175     a.strAssign(‘abcdefg‘);
176     console.log(a + ‘‘);
177     b.strAssign(‘hijklmno‘);
178     console.log(b + ‘‘);
179     c.strAssign(‘abcdefg‘);
180     console.log(a.strCompare(b));
181     console.log(a.strCompare(c));
182     var t = a.concat(b);
183     console.log(t + ‘‘);
184     t = t.substring(2, 5);
185     console.log(t + ‘‘);
javascript实现数据结构: 串的块链存储表示

 

单元测试代码:

javascript实现数据结构: 串的块链存储表示
 1 describe(‘LString tests‘, function(){
 2     var a = new LString(5);
 3     var b = new LString(4);
 4     var c = new LString(5);
 5     var t;
 6 
 7     it(‘should assign string‘, function(){
 8         a.strAssign(‘abcdefg‘);
 9         expect(a + ‘‘).toBe(‘abcdefg‘);
10 
11         b.strAssign(‘hijklmno‘);
12         expect(b + ‘‘).toBe(‘hijklmno‘);
13 
14         c.strAssign(‘abcdefg‘);
15         expect(c + ‘‘).toBe(‘abcdefg‘);
16     });
17 
18     it(‘should compare‘, function(){
19         expect(a.strCompare(b)).toBe(false);
20         expect(a.strCompare(c)).toBe(true);
21     });
22 
23     it(‘should concat‘, function(){
24         t = a.concat(b);
25         expect(t + ‘‘).toBe(‘abcdefghijklmno‘);
26     });
27 
28     it(‘should substring‘, function(){
29         t = t.substring(2, 5);
30         expect(t + ‘‘).toBe(‘cdefg‘);
31     });
32 });
View Code

 

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javascript实现数据结构: 串的块链存储表示

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