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Unsorted Lists
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  1. Unsorted Lists CS 308 – Data Structures

  2. What is a list? • A list is a homogeneous collection of elements. • Linear relationship between elements: (1) Each element except the first one has a unique predecessor. (2) Each element except the last one has a unique successor. • Length: the number of items in the list.

  3. What is an unsorted list? • A list in which data items are placed in no particular order. What is a sorted list? • A list in which data items are placed in a particular order. • Key: a member of the class whose value is used to determine the order ofthe items in the list.

  4. Operations • MakeEmpty • Boolean IsFull • int LengthIs • RetrieveItem (ItemType& item, Boolean& found) • InsertItem (ItemType item) • DeleteItem (ItemType item) • ResetList • void GetNextItem (ItemType& item)

  5. RetrieveItem (ItemType& item, Boolean& found) • Function: Retrieves list element whose key matches item's key (if present). • Preconditions: (1) List has been initialized, (2) Key member of item has been initialized. • Postconditions: (1) If there is an element someItem whose keymatches item's key, then found=true and item is a copy of someItem; otherwise, found=false and item is unchanged,(2) List is unchanged.

  6. InsertItem (ItemType item) • Function: Adds item to list • Preconditions: (1) List has been initialized, (2) List is not full, (3) item is not in list. • Postconditions: item is in list.

  7. DeleteItem (ItemType item) • Function: Deletes the element whose key matches item's key • Preconditions: (1) List has been initialized, (2) Key member of item has been initialized, (3) There is only one element in list which has a key matching item's key. • Postconditions: No element in list has a key matching item'skey.

  8. Unsorted List Implementation template<class ItemType> class UnsortedType { public: void MakeEmpty(); bool IsFull() const; int LengthIs() const; void RetrieveItem(ItemType&, bool&); void InsertItem(ItemType); void DeleteItem(ItemType); void ResetList(); bool IsLastItem() void GetNextItem(ItemType&); private: int length; ItemType info[MAX_ITEMS]; int currentPos; };

  9. Unsorted List Implementation (cont.) template<class ItemType> void UnsortedType<ItemType>::MakeEmpty() { length = 0; } template<class ItemType> bool UnsortedType<ItemType>::IsFull() const { return (length == MAX_ITEMS); } template<class ItemType> int UnsortedType<ItemType>::LengthIs() const { return length; }

  10. Unsorted List Implementation (cont.) template<class ItemType> void UnsortedType<ItemType>::RetrieveItem (ItemType& item, bool& found) { int location = 0; found = false; while( (location < length) && !found) if (item == info[location]) { found = true; item = info[location]; } else location++; }

  11. Unsorted List Implementation (cont.) template<class ItemType> void UnsortedType<ItemType>::InsertItem (ItemType item) { info[length] = item; length++; }

  12. Unsorted List Implementation (cont.) template<class ItemType> void UnsortedType<ItemType>::DeleteItem(ItemType item) { int location = 0; while(item != info[location]) location++; info[location] = info[length - 1]; length--; }

  13. Unsorted List Implementation (cont.) template<class ItemType> void UnsortedType<ItemType>::ResetList() { currentPos = -1; } template<class ItemType> bool UnsortedType<ItemType>::IsLastItem() { return(currentPos == length - 1); } template<class ItemType> void UnsortedType<ItemType>::GetNextItem (ItemType& item) { currentPos++; item = info[currentPos]; }

  14. Write a client function that splits an unsorted list into two unsorted lists using the following specification. SplitLists (UnsortedType list, ItemType item, UnsortedType& list1, UnsortedType& list 2) Function: Divides list into two lists according to the key of item. Preconditions: list has been initialized and is not empty. Postconditions: list1 contains all the items of list whose keys are less than or equal to item’s key. list2 contains all the items of list whose keys are greater than item’s key.

  15. ItemType listItem; list.ResetList(); while ( !list.IsLastItem()) { list.GetNextItem(listItem); if(listItem > item) { if (!list2.IsFull()) list2.InsertItem(listItem); } else { if ( !list1.IsFull()) list1.InsertItem(listItem); } }

  16. Exercises • 1, 9