ISC Practical 2027: Digital Lock Security Code Analyzer – Algorithm and Java Program

import java.util.Scanner;

/**
 * ISC Practical 2027 - Sample Paper 2, Question 3
 * Analyses the digits of a 5 to 10 digit security code of a digital lock.
 */
public class SecurityCode
{
    long code;           // the security code (long, because 10 digits exceed the int range)
    int dig[];           // digits from left to right
    int len;             // number of digits

    SecurityCode(long c)
    {
        code = c;
    }

    // stores the digits in dig[] from left to right
    void extractDigits()
    {
        String s = Long.toString(code);
        len = s.length();
        dig = new int[len];
        for (int i = 0; i < len; i++)
            dig[i] = s.charAt(i) - '0';
    }

    void analyse()
    {
        if (code <= 0 || Long.toString(code).length() < 5 || Long.toString(code).length() > 10)
        {
            System.out.println("INVALID INPUT");
            return;
        }
        extractDigits();
        int oddSum = 0, evenSum = 0;
        long product = 1;
        int freq[] = new int[10];               // freq[d] = how many times digit d occurs
        for (int i = 0; i < len; i++)
        {
            if ((i + 1) % 2 == 1)               // positions are counted from 1, left to right
                oddSum += dig[i];
            else
                evenSum += dig[i];
            if (dig[i] != 0)
                product *= dig[i];
            freq[dig[i]]++;
        }

        System.out.println("FIRST DIGIT: " + dig[0]);
        System.out.println("LAST DIGIT: " + dig[len - 1]);
        System.out.println("SUM OF ODD POSITION DIGITS: " + oddSum);
        System.out.println("SUM OF EVEN POSITION DIGITS: " + evenSum);
        System.out.println("PRODUCT OF NON-ZERO DIGITS: " + product);
        System.out.println("DIGIT FREQUENCY:");
        int most = 0, repeated = 0;
        for (int d = 0; d <= 9; d++)
        {
            if (freq[d] > 0)
                System.out.println("    " + d + ": " + freq[d]);
            if (freq[d] > freq[most])           // strict > keeps the smallest digit on a tie
                most = d;
            if (freq[d] > 1)
                repeated++;
        }
        System.out.println("MOST FREQUENT DIGIT: " + most);
        String type;
        if (repeated == 0)
            type = "STRONG CODE";
        else if (repeated == 1)
            type = "MODERATE CODE";
        else
            type = "WEAK CODE";
        System.out.println("CLASSIFICATION: " + type);
    }

    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter the security code: ");
        SecurityCode ob = new SecurityCode(sc.nextLong());
        ob.analyse();
    }
}

Name             Type       Purpose
---------------  ---------  -------
code             long       security code entered
dig[]            int[]      digits from left to right
len              int        number of digits
oddSum, evenSum  int        sums of odd and even position digits
product          long       product of non-zero digits
freq[]           int[]      freq[d] = occurrences of digit d
most             int        most frequent digit
repeated         int        how many digits occur more than once

INPUT:
5834271

OUTPUT:
FIRST DIGIT: 5
LAST DIGIT: 1
SUM OF ODD POSITION DIGITS: 11
SUM OF EVEN POSITION DIGITS: 19
PRODUCT OF NON-ZERO DIGITS: 6720
DIGIT FREQUENCY:
    1: 1
    2: 1
    3: 1
    4: 1
    5: 1
    7: 1
    8: 1
MOST FREQUENT DIGIT: 1
CLASSIFICATION: STRONG CODE

INPUT:
123455

OUTPUT:
FIRST DIGIT: 1
LAST DIGIT: 5
SUM OF ODD POSITION DIGITS: 9
SUM OF EVEN POSITION DIGITS: 11
PRODUCT OF NON-ZERO DIGITS: 600
DIGIT FREQUENCY:
    1: 1
    2: 1
    3: 1
    4: 1
    5: 2
MOST FREQUENT DIGIT: 5
CLASSIFICATION: MODERATE CODE

INPUT:
75523755

OUTPUT:
FIRST DIGIT: 7
LAST DIGIT: 5
SUM OF ODD POSITION DIGITS: 20
SUM OF EVEN POSITION DIGITS: 19
PRODUCT OF NON-ZERO DIGITS: 183750
DIGIT FREQUENCY:
    2: 1
    3: 1
    5: 4
    7: 2
MOST FREQUENT DIGIT: 5
CLASSIFICATION: WEAK CODE

INPUT:
542

OUTPUT:
INVALID INPUT

INPUT:
9876543210

OUTPUT:
FIRST DIGIT: 9
LAST DIGIT: 0
SUM OF ODD POSITION DIGITS: 25
SUM OF EVEN POSITION DIGITS: 20
PRODUCT OF NON-ZERO DIGITS: 362880
DIGIT FREQUENCY:
    0: 1
    1: 1
    2: 1
    3: 1
    4: 1
    5: 1
    6: 1
    7: 1
    8: 1
    9: 1
MOST FREQUENT DIGIT: 0
CLASSIFICATION: STRONG CODE

INPUT:
9988776655

OUTPUT:
FIRST DIGIT: 9
LAST DIGIT: 5
SUM OF ODD POSITION DIGITS: 35
SUM OF EVEN POSITION DIGITS: 35
PRODUCT OF NON-ZERO DIGITS: 228614400
DIGIT FREQUENCY:
    5: 2
    6: 2
    7: 2
    8: 2
    9: 2
MOST FREQUENT DIGIT: 5
CLASSIFICATION: WEAK CODE

INPUT:
12345678901

OUTPUT:
INVALID INPUT