Princeton University algorithm class algorithm part I week 3 comparator comparators

Comparator interface: sort by optional order

Public interface comparator <key> int compare (Key V, key W) // compare elements v and W

 

Example:

Java System sorting)

• Create comparator object)
• Pass the second parameter to array. Sort ()

String [] ;... arrays. sort (); // natural order (natural order )... arrays. sort (A, String. case_insensitive_order); arrays. sort (A, collator. getinstance (New locale ("es"); arrays. sort (A, new briishphonebookorder (); // these three sequence parameters are defined by the comparato <string> object.

 

Use the comparator interface to select and sort (insertion sort)

public static void sort(Object[] a, Comparator comparator){    int N = a.length;    for (int i = 0; i < N;i++)        for(int j =  i; j > 0 && less(comparator, a[j], a[j-1]); j--)            exch(a, j, j-1);        }private static boolean less(Comparator c, Object v, Object w){    return c.compare(v, w) < 0;    }private static void exch(Object[] a, int i, int j){    Object swap = a[i]; a[i] = a[j]; a[j] = swap;    }

Implement the comparator Interface

• Define the class that implements the comparator Interface
• Implement the compare () method

Public class student {public static final comparator <student> by_name = new byname (); public static final comparator <student> by_section = new bysection (); private final string name; private Final int section ;... private Static class byname implements comparator <student> // The byname class implements the comparator interface {public int compare (student V, student W) {return v. name. compareto (W. name) ;}} Private Static class bysection implements comparator <student> // bysection implements the comparator interface {public int compare (student V, student W) {return v. section-w. section ;}}}

The actual comparison is in the Compare overload method.

The comparator interface is a shell that wraps the compare () method.

Princeton University algorithm class algorithm part I week 3 comparator comparators