堆分配存储表示
这种存储表示的特点是，仍以一组地址连续的存储单元存放串值字符序列，但它们的存储空间是在程序执行过程中动态分配而得。
结构图：
实现：
1 function HString(){ 2 this.ch = {}; 3 this.length = 0; 4 } 5 exports.HString = HString; 6 HString.prototype = { 7 // 1 <= position <= this.length.在串的第position个字符之前插入串tHString 8 strInsert: function(position, tHString){ 9 if(position < 1 || position > this.length + 1) 10 throw new Error(‘unexpected position‘); 11 12 if(tHString.length){ 13 // 为插入t而腾出位置 14 for(var i = this.length - 1, len = position - 1; i >= len; --i) 15 this.ch[i + tHString.length] = this.ch[i]; 16 // s.ch[position - 1..position + tHString.length - 2] = tHString.ch[0..tHString.length - 1]; 17 // for(i = 0, len = tHString.length - 1; i <= len; i++) 18 // this.ch[position - 1 + i] = tHString.ch[i]; 19 stringCopy(this.ch, tHString.ch, position - 1, tHString.length - 1, 0); 20 21 this.length += tHString.length; 22 } 23 }, 24 strAssign: function(chars){ 25 // for(var i = 0, len = chars.length; i < len; i++){ 26 // this.ch[i] = chars[i]; 27 // } 28 stringCopy(this.ch, chars, 0, chars.length - 1, 0); 29 this.length = chars.length; 30 }, 31 strLength: function(){ 32 return this.length; 33 }, 34 strCompare: function(tHString){ 35 for(var i = 0, len = this.length; i < len && i < tHString.length; i++) 36 if(this.ch[i] !== tHString.ch[i]) return this.ch[i] - tHString.ch[i]; 37 38 return this.length - tHString.length; 39 }, 40 clearString: function(){ 41 this.ch = {}; 42 this.length = 0; 43 }, 44 concat: function(s){ 45 var t = new HString(); 46 47 // t.ch[0..this.length - 1] = this.ch[0..this.length - 1] 48 stringCopy(t.ch, this.ch, 0, this.length - 1, 0); 49 t.length = this.length + s.length; 50 // t.ch[this.length..t.length - 1] = s.ch[0..s.length - 1] 51 stringCopy(t.ch, s.ch, this.length, s.length - 1, 0); 52 53 return t; 54 }, 55 substring: function(position, len){ 56 position = ~~position || 0; 57 len = ~~len || this.length; 58 if(position < 0 || position > this.length - 1 || len < 0 || len > this.length - position) 59 throw new Error(‘unexpected paramater‘); 60 61 var sub = new HString(); 62 stringCopy(sub.ch, this.ch, 0, len - 1, position); 63 sub.length = len; 64 65 return sub; 66 }, 67 toString: function(){ 68 var s = ‘‘; 69 for(var i = 0, len = this.length; i < len; i++){ 70 s += this.ch[i]; 71 } 72 return s; 73 } 74 }; 75 76 function stringCopy(destination, target, destStart, length, targetStart){ 77 destStart = destStart || 0; 78 length = length || target.length; 79 targetStart = targetStart || 0; 80 81 for(var i = 0; i <= length; i++ ){ 82 destination[destStart + i] = target[targetStart + i]; 83 } 84 }
单元测试：
1 describe(‘HString tests‘, function(){ 2 var s = new HString(); 3 var t = new HString(); 4 5 it(‘should assign chars‘, function(){ 6 s.strAssign(‘hello world!‘); 7 expect(s + ‘‘).toBe(‘hello world!‘); 8 9 t.strAssign(‘jesus ‘); 10 expect(t + ‘‘).toBe(‘jesus ‘); 11 }); 12 13 it(‘should insert string into s‘, function(){ 14 s.strInsert(7, t); 15 expect(s + ‘‘).toBe(‘hello jesus world!‘); 16 }); 17 18 it(‘should concat string‘, function(){ 19 var ret = s.concat(t); 20 expect(ret + ‘‘).toBe(‘hello jesus world!jesus ‘); 21 }); 22 23 it(‘should get substring‘, function(){ 24 var ret = s.substring(0); 25 expect(ret + ‘‘).toBe(‘hello jesus world!‘); 26 27 ret = s.substring(5, 13); 28 expect(ret + ‘‘).toBe(‘ jesus world!‘); 29 30 ret = s.substring(3, 8); 31 expect(ret + ‘‘).toBe(‘lo jesus‘); 32 }); 33 });