//ProjectEuler/Java/Problem4.java
//Matthew Ellison
// Created: 03-01-19
//Modified: 03-28-19
//Find the largest palindrome made from the product of two 3-digit numbers
//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/JavaClasses
/*
	Copyright (C) 2019  Matthew Ellison

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/


import mattrixwv.Stopwatch;
import mattrixwv.Algorithms;

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


public class Problem4{
	private static final Integer START_NUM = 100;	//The first number to be multiplied
	private static final Integer END_NUM = 999;	//THe last number to be multiplied
	public static void main(String[] argv){
		Stopwatch timer = new Stopwatch();	//To time the execution time of this algorithm

		//Start the timer
		timer.start();

		ArrayList<Integer> palindromes = new ArrayList<Integer>();

		//Start at the first 3-digit number and check every one up to the last 3-digit number
		for(Integer firstNum = START_NUM;firstNum <= END_NUM;++firstNum){
			//You can start at the locatio of the first number because everything before that has already been tested. (100 * 101 == 101*100)
			for(Integer secondNum = firstNum;secondNum < END_NUM;++secondNum){
				//Get the product
				Integer product = firstNum * secondNum;
				//Change the number into a string
				String productString = product.toString();
				//Reverse the string
				String reverseString = new StringBuilder(productString).reverse().toString();
				
				//If the number and it's reverse are the same it is a palindrome so add it to the list
				if(productString.equals(reverseString)){
					palindromes.add(product);
				}
				else{
					//System.out.println("ProductString = " + productString);
					//System.out.println("reverseString = " + reverseString);
				}
				//If it's not a palindrome ignore it and move to the next number
			}
		}

		//Stop the timer
		timer.stop();

		//Sort the palindromes so that the last one is the largest
		Collections.sort(palindromes);

		//Print the results
		System.out.printf("The largest palindrome is %d\n", palindromes.get(palindromes.size() - 1));
		System.out.printf("It took " + timer.getStr() + " to run this algorithm\n");
	}
}

/* Results:
The largest palindrome is 906609
It took 105.376 milliseconds to run this algorithm
*/