CMSC 341

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CMSC 341

• Lists 3

2
Doubly-Linked Lists

• Option add pointer to previous node
• Issues
• doubles number of pointers
• allows immediate (O(1)) access to previous node

3
Circular Linked Lists

• Configurations
• header in circle
• header before circle
• no header

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Doubly-Linked Circular Linked List

• May or may not have a header
• Useful for applications requiring fast access to
  head and tail

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Vector Implementation

• template ltclass Objectgt
• void ListltObjectgt
• insert(const Object x, const ListItrltObjectgt p)
• if (!p.isPastEnd())
• // shift all elements down
• for (i this.last i gt p.current1 i--)
• nodesi 1 nodesi
• // put new element in hole
• nodesp.current 1 x

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Cursor Implementation

• Linked list look feel
• data stored as collection of nodes data and next
• nodes allocated and deallocated
• without dynamic memory allocation
• Basic concepts
• have node pool of all nodes, keep list of free
  ones
• use pool indices in place of pointers 0 NULL

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Cursor List Class

• template ltclass Objectgt
• class List
• List()
• // same old list public interface
• public
• struct CursorNode
• CursorNode() next(0)
• private
• CursorNode(const Object theElement, int n)
• element(theElement), next(n)
• Object element
• int next
• friend class ListltObjectgt
• friend class ListItrltObjectgt

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Cursor List Class (cont.)

• private
• int header
• static vectorltCursorNodegt cursorSpace
• static void initializeCursorSpace( )
• static int alloc( )
• static void free (int p)
• friend class ListItrltObjectgt

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Cursor Initialization

• template ltclass Objectgt
• void ListltObjectgtinitializeCursorSpace()
• static int cursorSpaceIsInitialized false
• if (!cursorSpaceIsInitialized)
• cursorSpace.resize(100)
• for(int i 0 i lt cursorSpace.size() i)
• cursorSpacei.next i 1
• cursorSpacecursorSpace.size()-1.next 0
• cursorSpaceIsInitialized true

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cursorSpace
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Cursor Allocation

• template ltclass Objectgt
• void ListltObjectgtalloc()
• int p cursorSpace0.next
• cursorSpace0.next cursorSpacep.next
• return p
• template ltclass Objectgt
• void ListltObjectgtfree(int p)
• cursorSpacep.next cursorSpace0.next
• cursorSpace0.next p

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Cursor Implementation (cont.)

• template ltclass Objectgt
• ListItrltObjectgt ListltObjectgt
• find(const Object x) const
• int itr cursorSpaceheader.nextwhile
  (itr!0 cursorSpaceitr.element ! x)
• itr cursorSpaceitr.next
• return ListItrltObjectgt(itr)

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Cursor Implementation (cont.)

• template ltclass Objectgt
• void ListltObjectgt
• insert(const Object x, const ListItrltObjectgt p)
• if (!p.isPastEnd())
• int pos p.current
• int tmp alloc()
• cursorSpacetmp
• CursorNode(x, cursorSpacepos.next)
• cursorSpacepos.next tmp

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Cursor Implementation (cont.)

• template ltclass Objectgt
• void ListltObjectgt
• remove(const Object x)
• ListItrltObjectgt p findPrevious(x)
• int pos p.current
• if (cursorSpacepos.next ! 0)
• int tmp cursorSpacepos.next
• cursorSpacepos.next cursorSpacetmp.n
  ext
• free (tmp)

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Comparing Performance