PowerPrint

import java.util.InputMismatchException;
import java.util.Scanner;

public class PowerPrint
{
    // Unicode character codes for superscripts of {0, 1, 2,..., 9}
    public static final char[] SUPERS = {
        '\u2070', '\u00B9', '\u00B2', '\u00B3', '\u2074',
        '\u2075', '\u2076', '\u2077', '\u2078', '\u2079'
    };

    public static void main( String[] args ) {
        Scanner scan = new Scanner( System.in );

        int i = -1;     // initialize to indicate bad input
        String prompt = "an integer in the set {0, 1, 2,..., 2\u00B3\u00B9-1}.";
        System.out.println( "Enter " + prompt );
        // nextInt() fails for input outside of int range [-2³¹, 2³¹-1]
        try { i = scan.nextInt(); }
        // don't need to repair anything, since i already indicates bad input
        catch ( InputMismatchException e ) {;}
        // refuse input outside range [0,  2³¹-1]
        if (0 > i || 2147483647 < i) {
            System.out.println( "I said \"" + prompt.toUpperCase() +  "\" \nBye." );
            return;
        }

        System.out.println( getPowersOf2( i, 0, "" ));
    }

    // convert decimal integer in range [0, 2³¹-1] into String of
    // form: 2ⁿ + 2ⁿ⁻¹ + 2ⁿ⁻² +...+ 2⁰, e.g., 67 ==> 2⁶ + 2¹ + 2⁰
    public static String getPowersOf2( int i, int n, String s ) {
        // get integer portion of division by 2
        int r = i/2;
        // if current i has remainder under division by 2, - (1 == i%2) -
        // then there is component to be added to sum, i.e., 2ⁿ for
        // current value of n; if there's more processing to be done -
        // (0 < r) - add leading " + " to the String as well
        if (1 == i%2) s = ((0 < r) ? " + " : "") + "2" + getSuperscript( n ) + s;
        // if more to process, recurse - otherwise, return s
        return (0 < r) ? getPowersOf2( r, ++n, s ) : s;
    }
    // compose superscript n from elements of SUPERS
    public static String getSuperscript( int n ) {
        return ((9 < n) ? "" + SUPERS[ (int) Math.floor( n/10 ) ] : "") +
            SUPERS[ n%10 ];
    }

}