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Implementing a Map ADT using a linked list

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• Linked list
  • Recall:

  • Note:

    We use a doubly linked list to simplify deletion

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• Storing entries as data in the list
  • Map entries stored in a list:

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    Example Map content:

    { ("cs170", "Siva"),   ("cs171", "Li"),   ("cs323", "Cheung"),   ("cs355", "Cheung") }

    Implementation with list:

    public class ListElem { public String key; public String value; public ListElem prev; // Double linked list for easy deletion public ListElem next; public ListElem(String k, String v) { key = k; value = v; prev = null; next = null; } public String toString() { return( "(" + key + "," + value + ")" ); } } public class List { public ListElem head; public int N; public List() { head = null; // Start with empty list N = 0; } public int size() { return(N); } // ************************************************* // delete(p): delete p // ************************************************* public void delete(ListElem p) { ListElem prevElem, nextElem; if ( N == 0 ) { return ; // Nothing to delete } else if ( N == 1 ) // Delete last element ==> empty list { head = null; } else if ( p.prev == null ) // Delete FIRST element { System.out.println("Delete: " + p.key); nextElem = p.next; nextElem.prev = null; head = nextElem; // The second is the new "first element" } else if ( p.next == null ) // Delete LAST element { System.out.println("Delete: " + p.key); prevElem = p.prev; prevElem.next = null; } else // Delete a "middle element" { System.out.println("Delete: " + p.key); prevElem = p.prev; nextElem = p.next; nextElem.prev = p.prev; prevElem.next = p.next; } N--; } // ------------------------------- // insert(v): insert at head // ------------------------------- public void insert(ListElem p) { if ( N == 0 ) { p.next = null; p.prev = null; head = p; } else { p.next = head; p.prev = null; head.prev = p; head = p; } N++; } public String toString() { String r = ""; ListElem p; p = head; // Very important: start at first element r = r + "{"; while ( p != null ) { r = r + p + " "; p = p.next; } return(r); } }

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  • Example Program: (Demo above code)                                                
    • ListElem.java: click here
    • List.java: click here
    • TestList.java: click here

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• Extending the linked list with Map functionality
  • How to implement Map functionality as List operations

    int size() return(N) boolean isEmpty()             return(N == 0)           Value get(Key k) Traverse the linked list If some list element contains the key k, return the corresponding value Otherwise, return null Running time: O(N) Value put(Key k, Value v) Traverse the linked list If some list element contains the key k, then replace the corresponding value with the input v Otherwise, insert the entry (k, v) Running time: O(N) Value remove(Key k) Traverse the linked list If some list element contains the key k, then:              Delete that entry return the old value Otherwise, return null Running time: O(N) Set keySet() Traverse the linked list For each list element, add the key part to the result set Running time: O(N) Set values() For each list element, add the value part to the result set Running time: O(N) Set entrySet() For each list element, add the list element to the result set Running time: O(N)

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• Sample implementation of Map functionality using Linked List
  • The (List-based) Map class (using String typed key and String typed value):

    public class ListMap extends List { public int size() { return(N); } public boolean isEmpty() { return(N==0); } public String get(String k) { ListElem p; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) return( p.value ); } return(null); } public String put(String k, String v) { ListElem p; String old; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) { old = p.value; p.value = v; // Replace old value return( old ); } } /* ------------------------------- Not found, insert new entry ------------------------------- */ p = new ListElem(k, v); insert(p); return(null); } public String remove(String k) { ListElem p; String old; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) { old = p.value; delete(p); // Delete element return(old); // Return old value } } return(null); // Return "not found" } public Collection keySet() { LinkedList<String> r = new LinkedList<String>(); // One of the classes that implements // "Collection" is LinkedList ListElem p; for ( p = head; p != null; p = p.next ) { r.add( p.key ); } return(r); } public Collection values() { LinkedList<String> r = new LinkedList<String>(); // One of the classes that implements // "Collection" is LinkedList ListElem p; for ( p = head; p != null; p = p.next ) { r.add( p.value ); } return(r); } public Collection entrySet() { LinkedList<ListElem> r = new LinkedList<ListElem>(); // One of the classes that implements // "Collection" is LinkedList ListElem p; for ( p = head; p != null; p = p.next ) { r.add( p ); } return(r); } }

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  • Example Program: (Demo above code)                                                
    • ListElem.java: click here
    • List.java: click here
    • Map.java: click here

    • TestMap.java: click here

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• Storing arbitrary keys and values in a Map: parameterized data structures
  • We can use a generic class (a.k.a. class with parameters) to generalize the objects that can be stored in a map

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  • Defining a parameterized ListElem class:

    public class ListElem<KeyType, ValueType> // ListElem class with 2 parameters { public KeyType key; public ValueType value; public ListElem<KeyType,ValueType> prev; public ListElem<KeyType,ValueType> next; public ListElem(KeyType k, ValueType v) { key = k; value = v; prev = null; next = null; } public String toString() { return( "(" + key + "," + value + ")" ); } }

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  • A parameterized List class:

    public class List<KeyType, ValueType> { public ListElem<KeyType, ValueType> head; public int N; public List() { head = null; // Start with empty list N = 0; } // ************************************************* // delete(p): delete p // ************************************************* public void delete(ListElem<KeyType, ValueType> p) { ListElem<KeyType, ValueType> prevElem, nextElem; if ( N == 0 ) { return ; // Nothing to delete } else if ( N == 1 ) // Delete last element ==> empty list { head = null; } else if ( p.prev == null ) // Delete FIRST element { System.out.println("Delete: " + p.key); nextElem = p.next; nextElem.prev = null; head = nextElem; // The second is the new "first element" } else if ( p.next == null ) // Delete LAST element { System.out.println("Delete: " + p.key); prevElem = p.prev; prevElem.next = null; } else // Delete a "middle element" { System.out.println("Delete: " + p.key); prevElem = p.prev; nextElem = p.next; nextElem.prev = p.prev; prevElem.next = p.next; } N--; } // ------------------------------- // insert(v): insert at head // ------------------------------- public void insert(ListElem<KeyType, ValueType> p) { if ( N == 0 ) { p.next = null; p.prev = null; head = p; } else { p.next = head; p.prev = null; head.prev = p; head = p; } N++; } public String toString() { String r = ""; ListElem<KeyType, ValueType> p; p = head; // Very important: start at first element r = r + "{"; while ( p != null ) { r = r + p + " "; p = p.next; } return(r); } }

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  • How to use a poarameterized type:

    Instead of: DataType varName Use: DataType< Actual_Type, ... > varName

    Example:

    List<String, String> L1 = new List<String, String> () ; List<String, Integer> L2 = new List<String, Integer> () ;

    (Programs will a lot of these notation is terribly difficult to read...)

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  • Example Program: (Demo above code)                                                
    • Parameterized ListElem.java: click here
    • Parameterized List.java: click here

    • Parameterized TestList.java (String, String): click here
    • Parameterized TestList2.java (String, Integer): click here

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• A parameterized Map implementation using Linked List
  • A parameterized (List-based) Map class:

    public class ListMap<KeyType, ValueType> extends List<KeyType, ValueType> { public int size() { return(N); } public boolean isEmpty() { return(N==0); } public ValueType get(KeyType k) { ListElem<KeyType, ValueType> p; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) return( p.value ); } return(null); } public ValueType put(KeyType k, ValueType v) { ListElem<KeyType, ValueType> p; ValueType old; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) { old = p.value; p.value = v; // Replace old value return( old ); } } /* ------------------------------- Not found, insert new entry ------------------------------- */ p = new ListElem<KeyType, ValueType> (k, v); insert(p); return(null); } public ValueType remove(KeyType k) { ListElem<KeyType, ValueType> p; ValueType old; for ( p = head; p != null; p = p.next ) { if ( p.key.equals( k ) ) { old = p.value; delete(p); // Delete element return(old); // Return old value } } return(null); // Return "not found" } public Collection<KeyType> keySet() { LinkedList<KeyType> r = new LinkedList<KeyType>(); // One of the classes that implements // "Collection" is LinkedList ListElem<KeyType, ValueType> p; for ( p = head; p != null; p = p.next ) { r.add( p.key ); } return(r); } public Collection<ValueType> values() { LinkedList<ValueType> r = new LinkedList<ValueType>(); // One of the classes that implements // "Collection" is LinkedList ListElem<KeyType, ValueType> p; for ( p = head; p != null; p = p.next ) { r.add( p.value ); } return(r); } public Collection<ListElem<KeyType, ValueType>> entrySet() { LinkedList<ListElem<KeyType, ValueType>> r = new LinkedList<ListElem<KeyType, ValueType>>(); // One of the classes that implements // "Collection" is LinkedList ListElem<KeyType, ValueType> p; for ( p = head; p != null; p = p.next ) { r.add( p ); } return(r); } }

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  • Example Program: (Demo above code)                                                
    • Parameterized ListElem.java: click here
    • Parameterized List.java: click here
    • Parameterized Map.java: click here

    • Test program TestMap.java using (String, String): click here
    • Test program TestMap2.java using (String, Integer): click here
    • Test program TestMap3.java (count # occurence of words in argument) click here

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• Note on parameterized classes
  • Parameterized classes are more flexible

  • But, the syntax makes a program very difficult to read...

    I am more concern to teach data structures and algorithm to manage the data structure.

    I look at parameterized types as a hinderance to clarity

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  • For the sake of simplicity and clarity of presentation of the data structures and algorithms, I will use non-parameterized classes in the algorithms (as much as possible).

    The purpose of this course is:

    Algorithms and Data structure

    It's not above how to make programs safer using parameterized types

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    But I do want to show you how to convert a NON parameterized typed class into a parameterized typed one...

    So you can convert it yourself: you can parameterize every data structures taught in the rest of the course.

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• Performance analysis
  • Running time of the operations:

    get() = O(N) (N = #items in the map, we need to traverse the linked list to find the key) put() = O(N) (because put() will update the value if the key is found in the map, so we also need to traverse the linked list to find the key) remove() = O(N) (N = #items in the map, we need to traverse the linked list to find the key)