Index handler
Representation invariant
This abstract data structure is generic and parameterized by some value type [math]\displaystyle{ \mathcal{V} }[/math]. An object of an implementation of this abstract data structure is repesented by:
- A positive integral number [math]\displaystyle{ N }[/math].
- A subset [math]\displaystyle{ I }[/math] of [math]\displaystyle{ \{1,\ldots,N\} }[/math], the currently used indexes.
- A mapping [math]\displaystyle{ I\rightarrow\mathcal{V} }[/math].
Remarks:
- This abstract data structure may be viewed as a specific, quite restricted type of map.
- The returned indexes have to be managed outside this data structure. For example, in Dijkstra and Prim, it might be a good option to make the index a node attribute,
Method
Name: reserve index
Input: A value [math]\displaystyle{ V\in\mathcal{V} }[/math].
Precondition: [math]\displaystyle{ |I|\lt N }[/math].
Return value: One of the indexes not in [math]\displaystyle{ I }[/math].
Postcondition: The returned index is inserted in [math]\displaystyle{ I }[/math] and associated with [math]\displaystyle{ V }[/math].
Method
Name: release index
Input: An integral number [math]\displaystyle{ i }[/math].
Precondition: [math]\displaystyle{ i\in I }[/math].
Postcondition: [math]\displaystyle{ i }[/math] is extracted from [math]\displaystyle{ I }[/math], and the associated value is dropped.
Method
Name: get value
Input: An integral number [math]\displaystyle{ i }[/math].
Precondition: [math]\displaystyle{ i\in I }[/math].
Return value: The value currently associated with [math]\displaystyle{ i }[/math].
Method
Name: change value
Input: An integral number [math]\displaystyle{ i }[/math] and a value [math]\displaystyle{ V\in\mathcal{V} }[/math].
Precondition: [math]\displaystyle{ i\in I }[/math].
Postcondition: The value currently associated with [math]\displaystyle{ i }[/math] is overwritten by [math]\displaystyle{ V }[/math].