Largest Palindrom Product for Java

Question

I need a java class that will find the largest Palindrome product of two N digits numbers (N meaning any 0 to 10 digit numbers ie --> 10, 100, 1000 etc.)

If you need further explanation please tell me.

class FindPalindrome {

private:

    //multiplicand 1
    int number_one; 
    //multiplicand 2
    int number_two;
    //holds current product
    int current;
    //copy of current product copy so as the current var values is not manipulated as its original will be needed
    int copy;   
    //holds most recently discovered palindrome
    int palindrome; 
    //holds greatest palindrome discovered 
    int greatest;
    //as determined by number of digits for operand
    int upper_limit; 
    int lower_limit;

public:

    //Constructor
    FindPalindrome(int digits_requiered);

    //Accessors
    int Greatest_Palindrome_Found();

    //Mutators
    void Product_Generator();
    void Determine_if_Palindrome();  

};

FindPalindrome::FindPalindrome(int digits_requiered){

upper_limit = pow(10, digits_requiered) - 1;
lower_limit = pow(10, digits_requiered -1);

number_two = number_one = upper_limit;

 current = 0;
 copy = 0;  
 palindrome = 0;
 greatest = 0;

}

int FindPalindrome::Greatest_Palindrome_Found(){

return greatest;

}

void FindPalindrome::Product_Generator(){

while (number_one >= lower_limit) {
    number_two = upper_limit;
    while (number_two >= lower_limit) {
        if(number_one >= number_two)
        {   
            //test initial numbers to see if they generate palindrome
            Determine_if_Palindrome();
        }
        number_two = number_two - 1;            
    }
    number_one = number_one - 1;
}

}

void FindPalindrome:: Determine_if_Palindrome(){

//used in determining length of array and storing product into array
int array_length = 0;
//copy of array length so that original length value is still available
int array_length_cpy = 0;   
//vars for checking for palindrome properties
int head = 0;
int tail = 0;
int retrieve_one = 0;
int retrieve_two = 0;

current = number_one * number_two;
copy = current;

//get length of number and create array to hold number
while (copy != 0) {
    copy /= 10;
    ++array_length;
}

int store[array_length];

//restore to products value for extraction manipulations
copy = current;

array_length_cpy = array_length;
//extract digits from number and poopulate array
for (int i = array_length_cpy; i>0; --i) {
    store[i-1] = copy%10;
    copy/=10;
    --array_length_cpy;
}

//Compare last and first digits then move "inwards" comparing the digits
tail = array_length -1;

retrieve_one = store[head];
retrieve_two = store[tail];

if (retrieve_one == retrieve_two) {
    for (int i = (array_length/2); i > 0; --i) {
        tail = tail -1;
        head = head + 1;
        retrieve_one = store[head];
        retrieve_two = store[tail];

        if (retrieve_one != retrieve_two) {
            return;
        }
    }

    palindrome = current; //it is a palindrome

    //test for if it is the biggest one found yet
    if (current > greatest) {
        greatest = current;

    }
}     

}

This is what Ive come up with, but it keeps displaying values until it reaches the largest palindrome product and sometimes doesnt output correctly.

Answer 1

Largest Palindrom Product for Java

  public class Prob4 {



public static void main(String[] args) {
 int max = 0;

 for(int i = 100; i< 1000; i++)
{
  for(int j = 100; j < 1000; j++)
 {
  if (palindrome(i * j))
  {
 if((i*j) > max)
 max = i * j;

   }


  }

 }
  System.out.println(max);
  }

  public static boolean  palindrome(int a)
   {
    int acopy = a;
    int rev = 0;
    int rem;
    while(acopy !=0)
   {
    rem = acopy %10;
    rev = rev * 10 + rem;
    acopy = acopy / 10;

   }
   if(rev == a)
    return true;
  else
   return false;
 }

  }