Prerequisite : Partition allocation methods

Best fit allocates the process to a partition which is the smallest sufficient partition among the free available partitions.

**Example: **

Input : blockSize[] = {100, 500, 200, 300, 600}; processSize[] = {212, 417, 112, 426}; Output: Process No. Process Size Block no. 1 212 4 2 417 2 3 112 3 4 426 5

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 minimum block size that can be assigned to current process i.e., find min(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.

## C/C++

// C++ implementation of Best - Fit algorithm #include<bits/stdc++.h> using namespace std; // Function to allocate memory to blocks as per Best fit // algorithm void bestFit(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 bestIdx = -1; for (int j=0; j<m; j++) { if (blockSize[j] >= processSize[i]) { if (bestIdx == -1) bestIdx = j; else if (blockSize[bestIdx] > blockSize[j]) bestIdx = j; } } // If we could find a block for current process if (bestIdx != -1) { // allocate block j to p[i] process allocation[i] = bestIdx; // Reduce available memory in this block. blockSize[bestIdx] -= 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]); bestFit(blockSize, m, processSize, n); return 0 ; }

## Java

// Java implementation of Best - Fit algorithm public class GFG { // Method to allocate memory to blocks as per Best fit // algorithm static void bestFit(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 bestIdx = -1; for (int j=0; j<m; j++) { if (blockSize[j] >= processSize[i]) { if (bestIdx == -1) bestIdx = j; else if (blockSize[bestIdx] > blockSize[j]) bestIdx = j; } } // If we could find a block for current process if (bestIdx != -1) { // allocate block j to p[i] process allocation[i] = bestIdx; // Reduce available memory in this block. blockSize[bestIdx] -= 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; bestFit(blockSize, m, processSize, n); } }

Output:

Process No. Process Size Block no. 1 212 4 2 417 2 3 112 3 4 426 5

**Is Best-Fit really best?**

Although, best fit minimizes the wastage space, it consumes a lot of processor time for searching the block which is close to required size. Also, Best-fit may perform poorer than other algorithms in some cases. For example, see below exercise.

Example: Consider the requests from processes in given order 300K, 25K, 125K and 50K. Let there be two blocks of memory available of size 150K followed by a block size 350K.

**Best Fit:**

300K is allocated from block of size 350K. 50 is left in the block.

25K is allocated from the remaining 50K block. 25K is left in the block.

125K is allocated from 150 K block. 25K is left in this block also.

50K can’t be allocated even if there is 25K + 25K space available.

**First Fit:**

300K request is allocated from 350K block, 50K is left out.

25K is be allocated from 150K block, 125K is left out.

Then 125K and 50K are allocated to remaining left out partitions.

So, first fit can handle requests.

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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