Selection Sort

Selection.java

import java.util.Comparator;

public class Selection
{
    private Selection() { }

    public static void sort( Comparable[] a )
    {
        int n = a.length;

        for ( int i = 0; i < n; i++ )
        {
            int min = i;

            for ( int j = i + 1; j < n; j++ )
            {
                if ( less( a[ j ], a[ min ] ) ) min = j;
            }
            exch( a, i, min );
            assert isSorted( a, 0, i );
        }
        assert isSorted( a );
    }

    public static void sort( Object[] a, Comparator comparator )
    {
        int n = a.length;

        for ( int i = 0; i < n; i++ )
        {
            int min = i;
            
            for ( int j = i + 1; j < n; j++ )
            {
                if ( less( comparator, a[ j ], a[ min ] ) ) min = j;
            }
            exch( a, i, min );
            assert isSorted( a, comparator, 0, i );
        }
        assert isSorted( a, comparator );
    }
    
    private static boolean less( Comparable v, Comparable w )
    {
        return v.compareTo( w ) < 0;
    }

    private static boolean less( Comparator comparator, Object v, Object w )
    {
        return comparator.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;
    }

    private static boolean isSorted( Comparable[] a )
    {
        return isSorted( a, 0, a.length - 1 );
    }
        
    private static boolean isSorted( Comparable[] a, int lo, int hi )
    {
        for ( int i = lo + 1; i <= hi; i++ )
            if ( less( a[ i ], a[ i - 1 ] ) ) return false;
        return true;
    }

    private static boolean isSorted( Object[] a, Comparator comparator )
    {
        return isSorted( a, comparator, 0, a.length - 1 );
    }

    private static boolean isSorted( Object[] a, Comparator comparator, int lo, int hi )
    {
        for ( int i = lo + 1; i <= hi; i++ )
            if ( less( comparator, a[ i ], a[ i - 1 ] ) ) return false;
        return true;
    }

    private static void show( Comparable[] a )
    {
        for ( int i = 0; i < a.length; i++ )
        {
            StdOut.println( a[ i ] );
        }
    }

    public static void main( String[] args )
    {
        String[] a = StdIn.readAllStrings();
        Selection.sort( a );
        show( a );
    }
}