# Program for Best Fit algorithm in Memory Management using Linked List

• Difficulty Level : Expert
• Last Updated : 17 Jan, 2022

Best fit algorithm for memory management: The memory partition in which there is a minimum loss on the allocation of the process is the best-fit memory partition that is allocated to the process.
We have already discussed one best-fit algorithm using arrays in this article. However, here we are going to look into another approach using a linked list where the deletion of allocated nodes is also possible.
Examples:

```Input : blockSize[] = {100, 500, 200}
processSize[] = {95, 417, 112, 426}
Output :
Block with size 426 can't be allocated
Tag    Block ID    Size
0          0        95
1          1        417
2          2        112
After deleting node with tag id 1.
Tag    Block ID    Size
0        0         95
2        2        112
3        1        426```

Approach: The idea is to assign a unique tag id to each memory block. Each process of different sizes are given block id, which signifies to which memory block they belong to, and unique tag id to delete particular process to free up space. Create a free list of given memory block sizes and allocated list of processes.
Create allocated list:
Create an allocated list of given process sizes by finding the most appropriate or best memory block to allocate memory from. If the memory block is not found, then simply print it. Otherwise, create a node and add it to the allocated linked list.
Delete process:
Each process is given a unique tag id. Delete the process node from the allocated linked list to free up some space for other processes. After deleting, use the block id of the deleted node to increase the memory block size in the free list.
Below is the implementation of the approach:

## C++

 `// C++ implementation of program``// for best fit algorithm for memory``// management using linked list` `#include ``using` `namespace` `std;` `// Two global counters``int` `g = 0, k = 0;` `// Structure for free list``struct` `free` `{``    ``int` `tag;``    ``int` `size;``    ``struct` `free``* next;``}* free_head = NULL, *prev_free = NULL;` `// Structure for allocated list``struct` `alloc {``    ``int` `block_id;``    ``int` `tag;``    ``int` `size;``    ``struct` `alloc* next;``}* alloc_head = NULL, *prev_alloc = NULL;` `// Function to create free``// list with given sizes``void` `create_free(``int` `c)``{``    ``struct` `free``* p = (``struct` `free``*)``        ``malloc``(``sizeof``(``struct` `free``));``    ``p->size = c;``    ``p->tag = g;``    ``p->next = NULL;``    ``if` `(free_head == NULL)``        ``free_head = p;``    ``else``        ``prev_free->next = p;``    ``prev_free = p;``    ``g++;``}` `// Function to print free list which``// prints free blocks of given sizes``void` `print_free()``{``    ``struct` `free``* p = free_head;``    ``cout << ``"Tag\tSize\n"``;``    ``while` `(p != NULL) {``        ``cout << p->tag << ``"\t"``             ``<< p->size << ``"\n"``;``        ``p = p->next;``    ``}``}` `// Function to print allocated list which``// prints allocated blocks and their block ids``void` `print_alloc()``{``    ``struct` `alloc* p = alloc_head;``    ``cout << ``"Tag\tBlock ID\tSize\n"``;``    ``while` `(p != NULL) {``        ``cout << p->tag << ``"\t  "` `<< p->block_id``             ``<< ``"\t\t"` `<< p->size << ``"\n"``;``        ``p = p->next;``    ``}``}` `// Function to allocate memory to``// blocks as per Best fit algorithm``void` `create_alloc(``int` `c)``{``    ``// create node for process of given size``    ``struct` `alloc* q = (``struct` `alloc*)``        ``malloc``(``sizeof``(``struct` `alloc));``    ``q->size = c;``    ``q->tag = k;``    ``q->next = NULL;``    ``struct` `free``* p = free_head;` `    ``// Temporary node r of free``    ``// type to find the best and``    ``// most suitable free node to``    ``// allocate space``    ``struct` `free``* r = (``struct` `free``*)``        ``malloc``(``sizeof``(``struct` `free``));``    ``r->size = 99999;` `    ``// Loop to find best choice``    ``while` `(p != NULL) {``        ``if` `(q->size <= p->size) {``            ``if` `(p->size < r->size)``                ``r = p;``        ``}``        ``p = p->next;``    ``}` `    ``// Node found to allocate``    ``// space from``    ``if` `(r->size != 99999) {``        ``// Adding node to allocated list``        ``q->block_id = r->tag;``        ``r->size -= q->size;``        ``if` `(alloc_head == NULL)``            ``alloc_head = q;``        ``else` `{``            ``prev_alloc = alloc_head;``            ``while` `(prev_alloc->next != NULL)``                ``prev_alloc = prev_alloc->next;``            ``prev_alloc->next = q;``        ``}``        ``k++;``    ``}` `    ``// Node with size not found``    ``else``        ``cout << ``"Block with size "``             ``<< c << ``" can't be allocated\n"``;``}` `// Function to delete node from``// allocated list to free some space``void` `delete_alloc(``int` `t)``{``    ``// Standard delete function``    ``// of a linked list node``    ``struct` `alloc *p = alloc_head, *q = NULL;` `    ``// First, find the node according``    ``while` `(p != NULL)``    ``// to given tag id``    ``{``        ``if` `(p->tag == t)``            ``break``;``        ``q = p;``        ``p = p->next;``    ``}``    ``if` `(p == NULL)``        ``cout << ``"Tag ID doesn't exist\n"``;``    ``else` `if` `(p == alloc_head)``        ``alloc_head = alloc_head->next;``    ``else``        ``q->next = p->next;``    ``struct` `free``* temp = free_head;``    ``while` `(temp != NULL) {``        ``if` `(temp->tag == p->block_id) {``            ``temp->size += p->size;``            ``break``;``        ``}``        ``temp = temp->next;``    ``}``}` `// Driver Code``int` `main()``{``    ``int` `blockSize[] = { 100, 500, 200 };``    ``int` `processSize[] = { 95, 417, 112, 426 };``    ``int` `m = ``sizeof``(blockSize)``            ``/ ``sizeof``(blockSize[0]);``    ``int` `n = ``sizeof``(processSize)``            ``/ ``sizeof``(processSize[0]);` `    ``for` `(``int` `i = 0; i < m; i++)``        ``create_free(blockSize[i]);` `    ``for` `(``int` `i = 0; i < n; i++)``        ``create_alloc(processSize[i]);` `    ``print_alloc();` `    ``// block of tag id 1 deleted``    ``// to free space for block of size 426``    ``delete_alloc(1);` `    ``create_alloc(426);``    ``cout << ``"After deleting block"``         ``<< ``" with tag id 1.\n"``;``    ``print_alloc();``}`

## Python3

 `# Python3 implementation of the First``# sit memory management algorithm``# using linked list` `# Two global counters``g ``=` `0``; k ``=` `0` `# Structure for free list``class` `free:``    ``def` `__init__(``self``):``        ``self``.tag``=``-``1``        ``self``.size``=``0``        ``self``.``next``=``None``free_head ``=` `None``; prev_free ``=` `None` `# Structure for allocated list``class` `alloc:``    ``def` `__init__(``self``):``        ``self``.block_id``=``-``1``        ``self``.tag``=``-``1``        ``self``.size``=``0``        ``self``.``next``=``None` `alloc_head ``=` `None``;prev_alloc ``=` `None` `# Function to create free``# list with given sizes``def` `create_free(c):``    ``global` `g,prev_free,free_head``    ``p ``=` `free()``    ``p.size ``=` `c``    ``p.tag ``=` `g``    ``p.``next` `=` `None``    ``if` `free_head ``is` `None``:``        ``free_head ``=` `p``    ``else``:``        ``prev_free.``next` `=` `p``    ``prev_free ``=` `p``    ``g``+``=``1`  `# Function to print free list which``# prints free blocks of given sizes``def` `print_free():``    ``p ``=` `free_head``    ``print``(``"Tag\tSize"``)``    ``while` `(p !``=` `None``) :``        ``print``(``"{}\t{}"``.``format``(p.tag,p.size))``        ``p ``=` `p.``next``    `   `# Function to print allocated list which``# prints allocated blocks and their block ids``def` `print_alloc():``    ``p ``=` `alloc_head``    ``print``(``"Tag\tBlock ID\tSize"``)``    ``while` `(p ``is` `not` `None``) :``        ``print``(``"{}\t{}\t{}\t"``.``format``(p.tag,p.block_id,p.size))``        ``p ``=` `p.``next``    `   `# Function to allocate memory to``# blocks as per First fit algorithm``def` `create_alloc(c):``    ``global` `k,alloc_head``    ``# create node for process of given size``    ``q ``=` `alloc()``    ``q.size ``=` `c``    ``q.tag ``=` `k``    ``q.``next` `=` `None``    ``p ``=` `free_head` `    ``# Iterate to find first memory``    ``# block with appropriate size``    ``while` `(p !``=` `None``) :``        ``if` `(q.size <``=` `p.size):``            ``break``        ``p ``=` `p.``next``    `  `    ``# Node found to allocate``    ``if` `(p !``=` `None``) :``        ``# Adding node to allocated list``        ``q.block_id ``=` `p.tag``        ``p.size ``-``=` `q.size``        ``if` `(alloc_head ``=``=` `None``):``            ``alloc_head ``=` `q``        ``else` `:``            ``prev_alloc ``=` `alloc_head``            ``while` `(prev_alloc.``next` `!``=` `None``):``                ``prev_alloc ``=` `prev_alloc.``next``            ``prev_alloc.``next` `=` `q``        ` `        ``k``+``=``1``    ` `    ``else``: ``# Node found to allocate space from``        ``print``(``"Block of size {} can't be allocated"``.``format``(c))` `# Function to delete node from``# allocated list to free some space``def` `delete_alloc(t):``    ``global` `alloc_head``    ``# Standard delete function``    ``# of a linked list node``    ``p ``=` `alloc_head; q ``=` `None` `    ``# First, find the node according``    ``# to given tag id``    ``while` `(p !``=` `None``) :``        ``if` `(p.tag ``=``=` `t):``            ``break``        ``q ``=` `p``        ``p ``=` `p.``next``    ` `    ``if` `(p ``=``=` `None``):``        ``print``(``"Tag ID doesn't exist"``)``    ``elif` `(p ``=``=` `alloc_head):``        ``alloc_head ``=` `alloc_head.``next``    ``else``:``        ``q.``next` `=` `p.``next``    ``temp ``=` `free_head``    ``while` `(temp !``=` `None``) :``        ``if` `(temp.tag ``=``=` `p.block_id) :``            ``temp.size ``+``=` `p.size``            ``break``        ` `        ``temp ``=` `temp.``next``    `   `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ``blockSize ``=` `[``100``, ``500``, ``200``]``    ``processSize ``=` `[``417``, ``112``, ``426``, ``95``]``    ``m ``=` `len``(blockSize)``    ``n ``=` `len``(processSize)` `    ``for` `i ``in` `range``(m):``        ``create_free(blockSize[i])` `    ``for` `i ``in` `range``(n):``        ``create_alloc(processSize[i])` `    ``print_alloc()` `    ``# Block of tag id 0 deleted``    ``# to free space for block of size 426``    ``delete_alloc(``0``)` `    ``create_alloc(``426``)``    ``print``(``"After deleting block with tag id 0."``)``    ``print_alloc()`

Output:

```Block with size 426 can't be allocated
Tag    Block ID    Size
0      0        95
1      1        417
2      2        112
After deleting block with tag id 1.
Tag    Block ID    Size
0      0        95
2      2        112
3      1        426```

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