ProjectEulerJava/src/main/java/com/mattrixwv/project_euler/problems/Problem23.java

//ProjectEulerJava/src/main/java/mattrixwv/ProjectEuler/Problems/Problem23.java
//Matthew Ellison
// Created: 03-22-19
//Modified: 06-27-23
//Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers
//Unless otherwise listed all non-standard includes are my own creation and available from https://bibucket.org/Mattrixwv/JavaClasses
/*
	Copyright (C) 2023  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/>.
*/
package com.mattrixwv.project_euler.problems;


import com.mattrixwv.ArrayAlgorithms;
import com.mattrixwv.NumberAlgorithms;

import java.util.ArrayList;
import java.util.List;


public class Problem23 extends Problem{
	//Variables
	//Static variables
	protected static int maxNum = 28123;	//The largest number to be checked
	//Instance variables
	protected ArrayList<Integer> divisorSums;	//This gives the sum of the divisors at subscripts
	protected long sum;	//The sum of all the numbers we are looking for


	//Functions
	//Constructor
	public Problem23(){
		super("Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers");
		divisorSums = new ArrayList<>();
		reserveArray();
		sum = 0;
	}
	//Operational functions
	//Reserve the size of the array to speed up insertion
	private void reserveArray(){
		divisorSums.ensureCapacity(maxNum);	//It is faster to reserve the appropriate amount of ram now
		//Make sure every element has a 0 in it's location
		while(divisorSums.size() <= maxNum){
			divisorSums.add(0);
		}
	}
	//Solve the problem
	@Override
	public void solve(){
		//If the problem has already been solved do nothing and end the function
		if(solved){
			return;
		}

		//Start the timer
		timer.start();


		//Get the sum of the divisors of all numbers < MAX_NUM
		for(int cnt = 1;cnt < maxNum;++cnt){
			List<Integer> div = NumberAlgorithms.getDivisors(cnt);
			//Remove the last element, which is the number itself. This gives us the propper divisors
			if(div.size() > 1){
				div.remove(div.size() - 1);
			}
			divisorSums.set(cnt, ArrayAlgorithms.getSum(div));
		}

		//Get the abundant numbers
		ArrayList<Integer> abund = new ArrayList<>();
		for(int cnt = 0;cnt < divisorSums.size();++cnt){
			if(divisorSums.get(cnt) > cnt){
				abund.add(cnt);
			}
		}

		//Check if each number can be the sum of 2 abundant numbers and add to the sum if no
		for(int cnt = 1;cnt < maxNum;++cnt){
			if(!isSum(abund, cnt)){
				sum += cnt;
			}
		}


		//Stop the timer
		timer.stop();

		//Throw a flag to show the problem is solved
		solved = true;
	}
	//A function that returns true if num can be created by adding two elements from abund and false if it cannot
	private boolean isSum(final ArrayList<Integer> abund, int num){
		int tempSum = 0;
		//Pick a number for the first part of the sum
		for(int firstNum = 0;firstNum < abund.size();++firstNum){
			//Pick a number for the second part of the sum
			for(int secondNum = firstNum;secondNum < abund.size();++secondNum){
				tempSum = abund.get(firstNum) + abund.get(secondNum);
				if(tempSum == num){
					return true;
				}
				else if(tempSum > num){
					break;
				}
			}
		}
		//If you have run through the entire list and did not find a sum then it is false
		return false;
	}
	//Reset the problem so it can be run again
	@Override
	public void reset(){
		super.reset();
		divisorSums.clear();
		reserveArray();
		sum = 0;
	}
	//Gets
	//Returns the result of solving the problem
	@Override
	public String getResult(){
		solvedCheck("result");
		return String.format("The answer is %d", sum);
	}
	//Returns the sum of the numbers asked for
	public long getSum(){
		solvedCheck("sum");
		return sum;
	}
}


/* Results:
The answer is 4179871
It took an average of 15.048 seconds to run this problem through 100 iterations
*/