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AnyBaseToAnyBase.java
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import java.util.Arrays;
import java.util.HashSet;
import java.util.InputMismatchException;
import java.util.Scanner;
/**
* Class for converting from "any" base to "any" other base, when "any" means from 2-36.
* Works by going from base 1 to decimal to base 2. Includes auxiliary method for
* determining whether a number is valid for a given base.
*
* @author Michael Rolland
* @version 2017.10.10
*
*/
public class AnyBaseToAnyBase {
// Smallest and largest base you want to accept as valid input
static final int MINIMUM_BASE = 2;
static final int MAXIMUM_BASE = 36;
// Driver
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String n;
int b1=0,b2=0;
while (true) {
try {
System.out.print("Enter number: ");
n = in.next();
System.out.print("Enter beginning base (between "+MINIMUM_BASE+" and "+MAXIMUM_BASE+"): ");
b1 = in.nextInt();
if (b1 > MAXIMUM_BASE || b1 < MINIMUM_BASE) {
System.out.println("Invalid base!");
continue;
}
if (!validForBase(n, b1)) {
System.out.println("The number is invalid for this base!");
continue;
}
System.out.print("Enter end base (between "+MINIMUM_BASE+" and "+MAXIMUM_BASE+"): ");
b2 = in.nextInt();
if (b2 > MAXIMUM_BASE || b2 < MINIMUM_BASE) {
System.out.println("Invalid base!");
continue;
}
break;
} catch (InputMismatchException e) {
System.out.println("Invalid input.");
in.next();
}
}
System.out.println(base2base(n, b1, b2));
}
/**
* Checks if a number (as a String) is valid for a given base.
*/
public static boolean validForBase(String n, int base) {
char[] validDigits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E',
'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
'W', 'X', 'Y', 'Z'};
// digitsForBase contains all the valid digits for the base given
char[] digitsForBase = Arrays.copyOfRange(validDigits, 0, base);
// Convert character array into set for convenience of contains() method
HashSet<Character> digitsList = new HashSet();
for (int i=0; i<digitsForBase.length; i++)
digitsList.add(digitsForBase[i]);
// Check that every digit in n is within the list of valid digits for that base.
for (char c : n.toCharArray())
if (!digitsList.contains(c))
return false;
return true;
}
/**
* Method to convert any integer from base b1 to base b2. Works by converting from b1 to decimal,
* then decimal to b2.
* @param n The integer to be converted.
* @param b1 Beginning base.
* @param b2 End base.
* @return n in base b2.
*/
public static String base2base(String n, int b1, int b2) {
// Declare variables: decimal value of n,
// character of base b1, character of base b2,
// and the string that will be returned.
int decimalValue = 0, charB2;
char charB1;
String output="";
// Go through every character of n
for (int i=0; i<n.length(); i++) {
// store the character in charB1
charB1 = n.charAt(i);
// if it is a non-number, convert it to a decimal value >9 and store it in charB2
if (charB1 >= 'A' && charB1 <= 'Z')
charB2 = 10 + (charB1 - 'A');
// Else, store the integer value in charB2
else
charB2 = charB1 - '0';
// Convert the digit to decimal and add it to the
// decimalValue of n
decimalValue = decimalValue * b1 + charB2;
}
// Converting the decimal value to base b2:
// A number is converted from decimal to another base
// by continuously dividing by the base and recording
// the remainder until the quotient is zero. The number in the
// new base is the remainders, with the last remainder
// being the left-most digit.
// While the quotient is NOT zero:
while (decimalValue != 0) {
// If the remainder is a digit < 10, simply add it to
// the left side of the new number.
if (decimalValue % b2 < 10)
output = Integer.toString(decimalValue % b2) + output;
// If the remainder is >= 10, add a character with the
// corresponding value to the new number. (A = 10, B = 11, C = 12, ...)
else
output = (char)((decimalValue % b2)+55) + output;
// Divide by the new base again
decimalValue /= b2;
}
return output;
}
}