Program for Worst Fit algorithm in Memory Management

Prerequisite : Partition allocation methods

Worst Fit allocates a process to the partition which is largest sufficient among the freely available partitions available in the main memory. If a large process comes at a later stage, then memory will not have space to accommodate it.

Example:

Input : blockSize[]   = {100, 500, 200, 300, 600};
        processSize[] = {212, 417, 112, 426};
Output:
Process No.    Process Size    Block no.
   1        212        5
   2        417        2
   3        112        5
   4        426        Not Allocated

first-fit



Implementation:
1- Input memory blocks and processes with sizes.
2- Initialize all memory blocks as free.
3- Start by picking each process and find the
   maximum block size that can be assigned to
   current process i.e., find max(bockSize[1], 
   blockSize[2],.....blockSize[n]) > 
   processSize[current], if found then assign 
   it to the current process.
5- If not then leave that process and keep checking
   the further processes.

Below is implementation of above steps.

C++

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// C++ implementation of worst - Fit algorithm
#include<bits/stdc++.h>
using namespace std;
  
// Function to allocate memory to blocks as per worst fit
// algorithm
void worstFit(int blockSize[], int m, int processSize[], 
                                                 int n)
{
    // Stores block id of the block allocated to a
    // process
    int allocation[n];
  
    // Initially no block is assigned to any process
    memset(allocation, -1, sizeof(allocation));
  
    // pick each process and find suitable blocks
    // according to its size ad assign to it
    for (int i=0; i<n; i++)
    {
        // Find the best fit block for current process
        int wstIdx = -1;
        for (int j=0; j<m; j++)
        {
            if (blockSize[j] >= processSize[i])
            {
                if (wstIdx == -1)
                    wstIdx = j;
                else if (blockSize[wstIdx] < blockSize[j])
                    wstIdx = j;
            }
        }
  
        // If we could find a block for current process
        if (wstIdx != -1)
        {
            // allocate block j to p[i] process
            allocation[i] = wstIdx;
  
            // Reduce available memory in this block.
            blockSize[wstIdx] -= processSize[i];
        }
    }
  
    cout << "\nProcess No.\tProcess Size\tBlock no.\n";
    for (int i = 0; i < n; i++)
    {
        cout << "   " << i+1 << "\t\t" << processSize[i] << "\t\t";
        if (allocation[i] != -1)
            cout << allocation[i] + 1;
        else
            cout << "Not Allocated";
        cout << endl;
    }
}
  
// Driver code
int main()
{
    int blockSize[] = {100, 500, 200, 300, 600};
    int processSize[] = {212, 417, 112, 426};
    int m = sizeof(blockSize)/sizeof(blockSize[0]);
    int n = sizeof(processSize)/sizeof(processSize[0]);
  
    worstFit(blockSize, m, processSize, n);
  
    return 0 ;
}

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Java

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// Java implementation of worst - Fit algorithm
  
public class GFG 
{
    // Method to allocate memory to blocks as per worst fit
    // algorithm
    static void worstFit(int blockSize[], int m, int processSize[], 
                                                     int n)
    {
        // Stores block id of the block allocated to a
        // process
        int allocation[] = new int[n];
       
        // Initially no block is assigned to any process
        for (int i = 0; i < allocation.length; i++)
            allocation[i] = -1;
       
        // pick each process and find suitable blocks
        // according to its size ad assign to it
        for (int i=0; i<n; i++)
        {
            // Find the best fit block for current process
            int wstIdx = -1;
            for (int j=0; j<m; j++)
            {
                if (blockSize[j] >= processSize[i])
                {
                    if (wstIdx == -1)
                        wstIdx = j;
                    else if (blockSize[wstIdx] < blockSize[j])
                        wstIdx = j;
                }
            }
       
            // If we could find a block for current process
            if (wstIdx != -1)
            {
                // allocate block j to p[i] process
                allocation[i] = wstIdx;
       
                // Reduce available memory in this block.
                blockSize[wstIdx] -= processSize[i];
            }
        }
       
        System.out.println("\nProcess No.\tProcess Size\tBlock no.");
        for (int i = 0; i < n; i++)
        {
            System.out.print("   " + (i+1) + "\t\t" + processSize[i] + "\t\t");
            if (allocation[i] != -1)
                System.out.print(allocation[i] + 1);
            else
                System.out.print("Not Allocated");
            System.out.println();
        }
    }
      
    // Driver Method
    public static void main(String[] args)
    {
         int blockSize[] = {100, 500, 200, 300, 600};
         int processSize[] = {212, 417, 112, 426};
         int m = blockSize.length;
         int n = processSize.length;
           
         worstFit(blockSize, m, processSize, n);
    }
}

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Python3

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# Python3 implementation of worst - Fit algorithm 
  
# Function to allocate memory to blocks as 
# per worst fit algorithm 
def worstFit(blockSize, m, processSize, n):
      
    # Stores block id of the block 
    # allocated to a process 
      
    # Initially no block is assigned 
    # to any process 
    allocation = [-1] * n
      
    # pick each process and find suitable blocks 
    # according to its size ad assign to it 
    for i in range(n):
          
        # Find the best fit block for 
        # current process 
        wstIdx = -1
        for j in range(m):
            if blockSize[j] >= processSize[i]:
                if wstIdx == -1
                    wstIdx =
                elif blockSize[wstIdx] < blockSize[j]: 
                    wstIdx = j
  
        # If we could find a block for 
        # current process 
        if wstIdx != -1:
              
            # allocate block j to p[i] process 
            allocation[i] = wstIdx 
  
            # Reduce available memory in this block. 
            blockSize[wstIdx] -= processSize[i]
  
    print("Process No. Process Size Block no.")
    for i in range(n):
        print(i + 1, "       "
              processSize[i], end = "    "
        if allocation[i] != -1:
            print(allocation[i] + 1
        else:
            print("Not Allocated")
  
# Driver code 
if __name__ == '__main__':
    blockSize = [100, 500, 200, 300, 600
    processSize = [212, 417, 112, 426
    m = len(blockSize) 
    n = len(processSize) 
  
    worstFit(blockSize, m, processSize, n)
  
# This code is contributed by PranchalK

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Output:

Process No.    Process Size    Block no.
   1        212        5
   2        417        2
   3        112        5
   4        426        Not Allocated

This article is contributed by Sahil Chhabra (akku). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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