ISBN-13 is a new standard for identifying books. It uses 13 digits d1d2d3d4d5d6d7d8d9d10d11d12d13. The last digit d13 is a check
sum, which is calculated from the other digits using the following formula: 10 - (d1 3d2 d3 3d4 d5 3d6 d7 3d8 d9 3d10 d11 3d12) % 10 If the checksum is 10, replace it with 0. Your program should read the input as a string.
1 answer:
Answer:
// Scanner class is imported to allow program
// read input from user
import java.util.Scanner;
// Solution class is created
public class Solution {
// main method that begin program execution
public static void main(String[] strings) {
// Scanner object scan is created
// it receive input via the keyboard
Scanner scan = new Scanner(System.in);
// a prompt is displayed for user to enter 12 digits of ISBN
System.out.print("Enter the first 12 digits of an ISBN as string: ");
// user input is assigned to input
String input = scan.next();
//if length of input is not 12, program display error message and quit
if (input.length() != 12) {
System.out.println(input + " is Invalid input");
System.exit(0);
}
// 0 is assigned to checkSum
int checkSum = 0;
// for loop that goes through the string and does the computation
for (int i = 0; i < input.length(); i++) {
// if the index is even
if ((i + 1) % 2 == 0) {
checkSum += (input.charAt(i) - '0') * 3;
}
// if the index is odd
else
{
checkSum += input.charAt(i) - '0';
}
}
// modulo 10 of checkSum is assigned to checkSum
checkSum %= 10;
// checkSum is substracted from 10
checkSum = 10 - checkSum;
// if checkSum equals 10, 0 is concatenated with input
// else input is concatenated with checkSum
if (checkSum == 10) input += "0";
else input += checkSum;
// the new value of the isbn-13 is displayed
System.out.println("The ISBN-13 number is " + input);
}
}
Explanation:
The program is written in Java and well commented.
A sample of program output during execution is also attached.
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Answer:
Here is the Python program.
def is_power(a, b): # function that takes two positive integers a and b as arguments
if a == b: #first base case: if both the numbers are equal
return True #returns True if a=b
elif b==1: #second base case: if the value of b is equal to 1
return False #returns False if b==1
else: #recursive step
return a%b==0 and is_power(a/b, b) #call divisible method and is_power method recursively to determine if the number is the power of another
Explanation:
return a%b==0 and is_power(a/b, b) statement basically means a number, a, is a power of b if it is divisible by b and a/b is a power of b
In the statement return a%b==0 and is_power(a/b, b) , a%b==0 checks whether a number a is completely divisible by number b. The % modulo operator is used to find the remainder of the division. If the remainder of the division is 0 it means that the number a is completely divisible by b otherwise it is not completely divisible.
The second part of the above statement calls is_power() method recursively. The and operator between the two means that both of the parts of the statement should be true in order to return true.
is_power() method takes two numbers a and b as arguments. First the method checks for two base cases. The first base case: a == b. Suppose the value of a = 1 and b =1 Then a is a power of b if both of them are equal. So this returns True if both a and b are equal.
Now the program checks its second base case b == 1. Lets say a is 10 and b is 1 Then the function returns False because there is no positive integer that is the power of 1 except 1 itself.
Now the recursive case return return a%b==0 and is_power(a/b, b) takes the modulo of a and b, and is_power method is called recursively in this statement. For example if a is 27 and b is 3 then this statement:
a%b==0 is True because 27 is completely divisible by 3 i.e. 27 % 3 = 0
is_power(a/b,b) is called. This method will be called recursively until the base condition is reached. You can see it has two arguments a/b and b. a/b = 27/3 = 9 So this becomes is_power(9,3)
The base cases are checked. Now this else statement is again executed return a%b==0 and is_power(a/b, b) as none of the above base cases is evaluated to true. when a%b==0 is True as 9 is completely divisible by 3 i.e. 9%3 =0 and is_power returns (9/3,3) which is (3,3). So this becomes is_power(3,3)
Now as value of a becomes 3 and value of b becomes 3. So the first base case a == b: condition now evaluates to true as 3=3. So it returns True.
Now in order to check the working of this function you can call this method as:
print(is_power(27, 3))
The output is:
True
