javascript实现数据结构：串--堆分配存储表示

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：

 function HString(){
     this.ch = {};
     this.length = 0;
   }
   exports.HString = HString;
   HString.prototype = {
     // 1 <= position <= this.length.在串的第position个字符之前插入串tHString
     strInsert: function(position, tHString){
       if(position < 1 || position > this.length + 1)
         throw new Error('unexpected position');

       if(tHString.length){
         // 为插入t而腾出位置
         for(var i = this.length - 1, len = position - 1; i >= len; --i)
           this.ch[i + tHString.length] = this.ch[i];
         // s.ch[position - 1..position + tHString.length - 2] = tHString.ch[0..tHString.length - 1];
 //        for(i = 0, len = tHString.length - 1; i <= len; i++)
 //          this.ch[position - 1 + i] = tHString.ch[i];
         stringCopy(this.ch, tHString.ch, position - 1, tHString.length - 1, 0);

         this.length += tHString.length;
       }
     },
     strAssign: function(chars){
 //      for(var i = 0, len = chars.length; i < len; i++){
 //        this.ch[i] = chars[i];
 //      }
       stringCopy(this.ch, chars, 0, chars.length - 1, 0);
       this.length = chars.length;
     },
     strLength: function(){
       return this.length;
     },
     strCompare: function(tHString){
       for(var i = 0, len = this.length; i < len && i < tHString.length; i++)
         if(this.ch[i] !== tHString.ch[i]) return this.ch[i] - tHString.ch[i];

       return this.length - tHString.length;
     },
     clearString: function(){
       this.ch = {};
       this.length = 0;
     },
     concat: function(s){
       var t = new HString();

       // t.ch[0..this.length - 1] = this.ch[0..this.length - 1]
       stringCopy(t.ch, this.ch, 0, this.length - 1, 0);
       t.length = this.length + s.length;
       // t.ch[this.length..t.length - 1] = s.ch[0..s.length - 1]
       stringCopy(t.ch, s.ch, this.length, s.length - 1, 0);

       return t;
     },
     substring: function(position, len){
       position = ~~position || 0;
       len = ~~len || this.length;
       if(position < 0 || position > this.length - 1 || len < 0 || len > this.length - position)
         throw new Error('unexpected paramater');

       var sub = new HString();
       stringCopy(sub.ch, this.ch, 0, len - 1, position);
       sub.length = len;

       return sub;
     },
     toString: function(){
       var s = '';
       for(var i = 0, len = this.length; i < len; i++){
         s += this.ch[i];
       }
       return s;
     }
   };

   function stringCopy(destination, target, destStart, length, targetStart){
     destStart = destStart || 0;
     length = length || target.length;
     targetStart = targetStart || 0;

     for(var i = 0; i <= length; i++ ){
       destination[destStart + i] = target[targetStart + i];
     }
   }

单元测试：

 describe('HString tests', function(){
   var s = new HString();
   var t = new HString();

   it('should assign chars', function(){
     s.strAssign('hello world!');
     expect(s + '').toBe('hello world!');

     t.strAssign('jesus ');
     expect(t + '').toBe('jesus ');
   });

   it('should insert string into s', function(){
     s.strInsert(7, t);
     expect(s + '').toBe('hello jesus world!');
   });

   it('should concat string', function(){
     var ret = s.concat(t);
     expect(ret + '').toBe('hello jesus world!jesus ');
   });

   it('should get substring', function(){
     var ret = s.substring(0);
     expect(ret + '').toBe('hello jesus world!');

     ret = s.substring(5, 13);
     expect(ret + '').toBe(' jesus world!');

     ret = s.substring(3, 8);
     expect(ret + '').toBe('lo jesus');
   });
 });