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82 lines
2.9 KiB
Java
82 lines
2.9 KiB
Java
//ProjectEuler/Java/Problem4.java
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//Matthew Ellison
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// Created: 03-01-19
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//Modified: 03-28-19
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//Find the largest palindrome made from the product of two 3-digit numbers
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//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/JavaClasses
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/*
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Copyright (C) 2019 Matthew Ellison
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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import mattrixwv.Stopwatch;
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import mattrixwv.Algorithms;
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import java.util.ArrayList;
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import java.util.Collections;
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public class Problem4{
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private static final Integer START_NUM = 100; //The first number to be multiplied
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private static final Integer END_NUM = 999; //THe last number to be multiplied
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public static void main(String[] argv){
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Stopwatch timer = new Stopwatch(); //To time the execution time of this algorithm
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//Start the timer
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timer.start();
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ArrayList<Integer> palindromes = new ArrayList<Integer>();
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//Start at the first 3-digit number and check every one up to the last 3-digit number
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for(Integer firstNum = START_NUM;firstNum <= END_NUM;++firstNum){
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//You can start at the locatio of the first number because everything before that has already been tested. (100 * 101 == 101*100)
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for(Integer secondNum = firstNum;secondNum < END_NUM;++secondNum){
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//Get the product
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Integer product = firstNum * secondNum;
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//Change the number into a string
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String productString = product.toString();
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//Reverse the string
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String reverseString = new StringBuilder(productString).reverse().toString();
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//If the number and it's reverse are the same it is a palindrome so add it to the list
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if(productString.equals(reverseString)){
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palindromes.add(product);
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}
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else{
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//System.out.println("ProductString = " + productString);
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//System.out.println("reverseString = " + reverseString);
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}
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//If it's not a palindrome ignore it and move to the next number
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}
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}
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//Stop the timer
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timer.stop();
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//Sort the palindromes so that the last one is the largest
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Collections.sort(palindromes);
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//Print the results
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System.out.printf("The largest palindrome is %d\n", palindromes.get(palindromes.size() - 1));
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System.out.printf("It took " + timer.getStr() + " to run this algorithm\n");
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}
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}
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/* Results:
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The largest palindrome is 906609
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It took 105.376 milliseconds to run this algorithm
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*/
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