MemoryManagementAlgorithms.java

package com.thealgorithms.others;

import java.util.ArrayList;
/**
 * @author Alexandros Lemonaris
 */
public abstract class MemoryManagementAlgorithms {

    /**
     * Method to allocate memory to blocks according to CPU algorithms.
     * Use of inheritance to avoid repeated code.
     * Abstract method since it is implemented different for each algorithm.
     * It should return an ArrayList of Integers, where the index is the process
     * ID (zero-indexed) and the value is the block number (also zero-indexed).
     * @param sizeOfBlocks an int array that contains the sizes of the memory
     * blocks available.
     * @param sizeOfProcesses: an int array that contains the sizes of the
     * processes we need memory blocks for.
     * @return the ArrayList filled with Integers repressenting the memory
     * allocation that took place.
     */
    public abstract ArrayList<Integer> fitProcess(int[] sizeOfBlocks, int[] sizeOfProcesses);

    /**
     * A constant value used to indicate that an allocation has not been made.
     * This value is used as a sentinel value to represent that no allocation has been made
     * when allocating space in an array or other data structure.
     * The value is -255 and is marked as protected and final to ensure that it cannot be modified
     * from outside the class and that its value remains consistent throughout the program
     * execution.
     *
     * @author: Ishan Makadia (github.com/intrepid-ishan)
     * @version: April 06, 2023
     */
    protected static final int NO_ALLOCATION = -255;
}

/**
 * @author Dekas Dimitrios
 */
class BestFitCPU extends MemoryManagementAlgorithms {

    /**
     * Method to find the maximum valued element of an array filled with
     * positive integers.
     *
     * @param array: an array filled with positive integers.
     * @return the maximum valued element of the array.
     */
    private static int findMaxElement(int[] array) {
        int max = -1;
        for (int value : array) {
            if (value > max) {
                max = value;
            }
        }
        return max;
    }

    /**
     * Method to find the index of the memory block that is going to fit the
     * given process based on the best fit algorithm.
     *
     * @param blocks: the array with the available memory blocks.
     * @param process: the size of the process.
     * @return the index of the block that fits, or -255 if no such block
     * exists.
     */
    private static int findBestFit(int[] blockSizes, int processSize) {
        // Initialize minDiff with an unreachable value by a difference between a blockSize and the
        // processSize.
        int minDiff = findMaxElement(blockSizes);
        int index = NO_ALLOCATION; // If there is no block that can fit the process, return
                                   // NO_ALLOCATION as the
        // result.
        for (int i = 0; i < blockSizes.length; i++) { // Find the most fitting memory block for the given process.
            if (blockSizes[i] - processSize < minDiff && blockSizes[i] - processSize >= 0) {
                minDiff = blockSizes[i] - processSize;
                index = i;
            }
        }
        return index;
    }

    /**
     * Method to allocate memory to blocks according to the best fit algorithm.
     * It should return an ArrayList of Integers, where the index is the process
     * ID (zero-indexed) and the value is the block number (also zero-indexed).
     *
     * @param sizeOfBlocks: an int array that contains the sizes of the memory
     * blocks available.
     * @param sizeOfProcesses: an int array that contains the sizes of the
     * processes we need memory blocks for.
     * @return the ArrayList filled with Integers repressenting the memory
     * allocation that took place.
     */
    public ArrayList<Integer> fitProcess(int[] sizeOfBlocks, int[] sizeOfProcesses) {
        // The array list responsible for saving the memory allocations done by the best-fit
        // algorithm
        ArrayList<Integer> memAlloc = new ArrayList<>();
        // Do this for every process
        for (int processSize : sizeOfProcesses) {
            int chosenBlockIdx = findBestFit(sizeOfBlocks, processSize); // Find the index of the memory block going to be used
            memAlloc.add(chosenBlockIdx); // Store the chosen block index in the memAlloc array list
            if (chosenBlockIdx != NO_ALLOCATION) { // Only if a block was chosen to store the process in it,
                sizeOfBlocks[chosenBlockIdx] -= processSize; // resize the block based on the process size
            }
        }
        return memAlloc;
    }
}

/**
 * @author Dekas Dimitrios
 */
class WorstFitCPU extends MemoryManagementAlgorithms {

    /**
     * Method to find the index of the memory block that is going to fit the
     * given process based on the worst fit algorithm.
     *
     * @param blocks: the array with the available memory blocks.
     * @param process: the size of the process.
     * @return the index of the block that fits, or -255 if no such block
     * exists.
     */
    private static int findWorstFit(int[] blockSizes, int processSize) {
        int max = -1;
        int index = -1;
        for (int i = 0; i < blockSizes.length; i++) { // Find the index of the biggest memory block available.
            if (blockSizes[i] > max) {
                max = blockSizes[i];
                index = i;
            }
        }
        // If the biggest memory block cannot fit the process, return -255 as the result
        if (processSize > blockSizes[index]) {
            return NO_ALLOCATION;
        }
        return index;
    }

    /**
     * Method to allocate memory to blocks according to the worst fit algorithm.
     * It should return an ArrayList of Integers, where the index is the process
     * ID (zero-indexed) and the value is the block number (also zero-indexed).
     *
     * @param sizeOfBlocks: an int array that contains the sizes of the memory
     * blocks available.
     * @param sizeOfProcesses: an int array that contains the sizes of the
     * processes we need memory blocks for.
     * @return the ArrayList filled with Integers repressenting the memory
     * allocation that took place.
     */
    public ArrayList<Integer> fitProcess(int[] sizeOfBlocks, int[] sizeOfProcesses) {
        // The array list responsible for saving the memory allocations done by the worst-fit
        // algorithm
        ArrayList<Integer> memAlloc = new ArrayList<>();
        // Do this for every process
        for (int processSize : sizeOfProcesses) {
            int chosenBlockIdx = findWorstFit(sizeOfBlocks, processSize); // Find the index of the memory block going to be used
            memAlloc.add(chosenBlockIdx); // Store the chosen block index in the memAlloc array list
            if (chosenBlockIdx != NO_ALLOCATION) { // Only if a block was chosen to store the process in it,
                sizeOfBlocks[chosenBlockIdx] -= processSize; // resize the block based on the process size
            }
        }
        return memAlloc;
    }
}

/**
 * @author Dekas Dimitrios
 */
class FirstFitCPU extends MemoryManagementAlgorithms {

    /**
     * Method to find the index of the memory block that is going to fit the
     * given process based on the first fit algorithm.
     *
     * @param blocks: the array with the available memory blocks.
     * @param process: the size of the process.
     * @return the index of the block that fits, or -255 if no such block
     * exists.
     */
    private static int findFirstFit(int[] blockSizes, int processSize) {
        for (int i = 0; i < blockSizes.length; i++) {
            if (blockSizes[i] >= processSize) {
                return i;
            }
        }
        // If there is not a block that can fit the process, return -255 as the result
        return NO_ALLOCATION;
    }

    /**
     * Method to allocate memory to blocks according to the first fit algorithm.
     * It should return an ArrayList of Integers, where the index is the process
     * ID (zero-indexed) and the value is the block number (also zero-indexed).
     *
     * @param sizeOfBlocks: an int array that contains the sizes of the memory
     * blocks available.
     * @param sizeOfProcesses: an int array that contains the sizes of the
     * processes we need memory blocks for.
     * @return the ArrayList filled with Integers repressenting the memory
     * allocation that took place.
     */
    public ArrayList<Integer> fitProcess(int[] sizeOfBlocks, int[] sizeOfProcesses) {
        // The array list responsible for saving the memory allocations done by the first-fit
        // algorithm
        ArrayList<Integer> memAlloc = new ArrayList<>();
        // Do this for every process
        for (int processSize : sizeOfProcesses) {
            int chosenBlockIdx = findFirstFit(sizeOfBlocks, processSize); // Find the index of the memory block going to be used
            memAlloc.add(chosenBlockIdx); // Store the chosen block index in the memAlloc array list
            if (chosenBlockIdx != NO_ALLOCATION) { // Only if a block was chosen to store the process in it,
                sizeOfBlocks[chosenBlockIdx] -= processSize; // resize the block based on the process size
            }
        }
        return memAlloc;
    }
}

/**
 * @author Alexandros Lemonaris
 */
class NextFit extends MemoryManagementAlgorithms {

    private int counter = 0; // variable that keeps the position of the last registration into the memory

    /**
     * Method to find the index of the memory block that is going to fit the
     * given process based on the next fit algorithm. In the case of next fit,
     * if the search is interrupted in between, the new search is carried out from the last
     * location.
     *
     * @param blocks: the array with the available memory blocks.
     * @param process: the size of the process.
     * @return the index of the block that fits, or -255 if no such block
     * exists.
     */
    private int findNextFit(int[] blockSizes, int processSize) {
        for (int i = 0; i < blockSizes.length; i++) {
            if (counter + i >= blockSizes.length) {
                counter = -i; // starts from the start of the array
            }
            if (blockSizes[i + counter] >= processSize) {
                counter += i;
                return counter;
            }
        }
        // If there is not a block that can fit the process, return -255 as the result
        counter += blockSizes.length; // counter keeps its last value
        return NO_ALLOCATION;
    }

    /**
     * Method to allocate memory to blocks according to the first fit algorithm.
     * It should return an ArrayList of Integers, where the index is the process
     * ID (zero-indexed) and the value is the block number (also zero-indexed).
     *
     * @param sizeOfBlocks: an int array that contains the sizes of the memory
     * blocks available.
     * @param sizeOfProcesses: an int array that contains the sizes of the
     * processes we need memory blocks for.
     * @return the ArrayList filled with Integers repressenting the memory
     * allocation that took place.
     */
    public ArrayList<Integer> fitProcess(int[] sizeOfBlocks, int[] sizeOfProcesses) {
        // The array list responsible for saving the memory allocations done by the first-fit
        // algorithm
        ArrayList<Integer> memAlloc = new ArrayList<>();
        // Do this for every process
        for (int processSize : sizeOfProcesses) {
            int chosenBlockIdx = findNextFit(sizeOfBlocks, processSize); // Find the index of the memory block going to be used
            memAlloc.add(chosenBlockIdx); // Store the chosen block index in the memAlloc array list
            if (chosenBlockIdx != NO_ALLOCATION) { // Only if a block was chosen to store the process in it,
                sizeOfBlocks[chosenBlockIdx] -= processSize; // resize the block based on the process size
            }
        }
        return memAlloc;
    }
}