Largest palindrome product - Java Algorithm

Java examples for Algorithm:Number

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Introduction

A palindromic number reads the same both ways.

The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 * 99.

Find the largest palindrome made from the product of two 3-digit numbers.

Demo Code


import java.util.ArrayList;
import java.util.Collections;

public class LargestPalindromeNumber {
  /* The first palindrome function is faster than the second. */
  /*public static boolean isPalindrome(int n){
    int temp = n, digit, rev = 0;//from w ww . j  a  v  a  2s. c o  m
    while(temp != 0){
      digit = temp % 10;
      rev = rev * 10 + digit;
      temp /= 10;
    }
    if(rev == n)
      return true;
    return false;
  }*/
  public static boolean isPalindrome(int n){
    String a = n + "";
    String b = new StringBuilder(a).reverse().toString();
    if(b.equals(a))
      return true;
    else
      return false;
  }
  public static void largestPalindromeNum(){
    ArrayList<Integer> arr = new ArrayList<Integer>();
    int i, j, result;
    for(i = 999; i >= 100; i--){
      for(j = 999; j >= i; j--){
        result = i * j;
        if(isPalindrome(result))
          arr.add(result);
      }
    }
    System.out.println(Collections.max(arr));
  }
  public static void main(String[] args) {
    largestPalindromeNum();
  }
}

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