JavaAlgorithms/Others/BestFit.java

package Others;

import java.util.ArrayList;

/**
 * @author Dekas Dimitrios
 */
public class BestFit {
    private static final int NO_ALLOCATION = -255; // if a process has been allocated in position -255,
                                                   // it means that it has not been actually allocated.

    /**
     * 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.
     */
    static ArrayList<Integer> bestFit(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;
    }

    /**
     * Method to print the memory allocated.
     *
     * @param memAllocation: an ArrayList of Integer representing the memory allocation done by the bestFit method.
     */
    public static void printMemoryAllocation(ArrayList<Integer> memAllocation) {
        System.out.println("Process No.\tBlock No.");
        System.out.println("===========\t=========");
        for (int i = 0; i < memAllocation.size(); i++) {
            System.out.print(" " + i + "\t\t");
            if (memAllocation.get(i) != NO_ALLOCATION)
                System.out.print(memAllocation.get(i));
            else
                System.out.print("Not Allocated");
            System.out.println();
        }
    }
}