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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++

// 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 << "
Process No.	Process Size	Block no.
"; 
    for (int i = 0; i < n; i++) 
    { 
        cout << "   " << i+1 << " " << processSize[i] << " "; 
        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 ; 
} 

Java

// 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("
Process No.	Process Size	Block no."); 
        for (int i = 0; i < n; i++) 
        { 
            System.out.print("   " + (i+1) + " " + processSize[i] + " "); 
            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); 
    } 
} 

/div>

Python3

# 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 = j  
                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 

Output:

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

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Program for Worst Fit algorithm in Memory Management

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

tags:

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