Code:
// C program for Huffman Coding
#include <stdio.h>
#include <stdlib.h>
// This constant can be avoided by explicitly calculating
height of Huffman Tree
#define MAX_TREE_HT 100
// A Huffman tree node
struct MinHeapNode
{
char
data; // One of the input characters
unsigned
freq; // Frequency of the character
struct
MinHeapNode *left, *right; // Left and right child of this node
};
// A Min Heap: Collection of min heap (or Hufmman tree)
nodes
struct MinHeap
{
unsigned
size; // Current size of min heap
unsigned
capacity; // capacity of min heap
struct
MinHeapNode **array; // Attay of minheap node pointers
};
// A utility function allocate a new min heap node with
given character
// and frequency of the character
struct MinHeapNode* newNode(char data, unsigned freq)
{
struct
MinHeapNode* temp =
(struct
MinHeapNode*) malloc(sizeof(struct MinHeapNode));
temp->left
= temp->right = NULL;
temp->data
= data;
temp->freq
= freq;
return
temp;
}
// A utility function to create a min heap of given capacity
struct MinHeap* createMinHeap(unsigned capacity)
{
struct
MinHeap* minHeap =
(struct
MinHeap*) malloc(sizeof(struct MinHeap));
minHeap->size
= 0; // current size is 0
minHeap->capacity
= capacity;
minHeap->array
=
(struct
MinHeapNode**)malloc(minHeap->capacity * sizeof(struct MinHeapNode*));
return
minHeap;
}
// A utility function to swap two min heap nodes
void swapMinHeapNode(struct MinHeapNode** a, struct
MinHeapNode** b)
{
struct
MinHeapNode* t = *a;
*a = *b;
*b = t;
}
// The standard minHeapify function.
void minHeapify(struct MinHeap* minHeap, int idx)
{
int
smallest = idx;
int
left = 2 * idx + 1;
int
right = 2 * idx + 2;
if
(left < minHeap->size &&
minHeap->array[left]->freq
< minHeap->array[smallest]->freq)
smallest
= left;
if
(right < minHeap->size &&
minHeap->array[right]->freq
< minHeap->array[smallest]->freq)
smallest
= right;
if
(smallest != idx)
{
swapMinHeapNode(&minHeap->array[smallest],
&minHeap->array[idx]);
minHeapify(minHeap,
smallest);
}
}
// A utility function to check if size of heap is 1 or not
int isSizeOne(struct MinHeap* minHeap)
{
return
(minHeap->size == 1);
}
// A standard function to extract minimum value node from
heap
struct MinHeapNode* extractMin(struct MinHeap* minHeap)
{
struct
MinHeapNode* temp = minHeap->array[0];
minHeap->array[0]
= minHeap->array[minHeap->size - 1];
--minHeap->size;
minHeapify(minHeap,
0);
return
temp;
}
// A utility function to insert a new node to Min Heap
void insertMinHeap(struct MinHeap* minHeap, struct
MinHeapNode* minHeapNode)
{
++minHeap->size;
int i =
minHeap->size - 1;
while
(i && minHeapNode->freq < minHeap->array[(i - 1)/2]->freq)
{
minHeap->array[i]
= minHeap->array[(i - 1)/2];
i
= (i - 1)/2;
}
minHeap->array[i]
= minHeapNode;
}
// A standard funvtion to build min heap
void buildMinHeap(struct MinHeap* minHeap)
{
int n =
minHeap->size - 1;
int i;
for (i
= (n - 1) / 2; i >= 0; --i)
minHeapify(minHeap,
i);
}
// A utility function to print an array of size n
void printArr(int arr[], int n)
{
int i;
for (i
= 0; i < n; ++i)
printf("%d",
arr[i]);
printf("\n");
}
// Utility function to check if this node is leaf
int isLeaf(struct MinHeapNode* root)
{
return
!(root->left) && !(root->right) ;
}
// Creates a min heap of capacity equal to size and inserts
all character of
// data[] in min heap. Initially size of min heap is equal
to capacity
struct MinHeap* createAndBuildMinHeap(char data[], int
freq[], int size)
{
struct
MinHeap* minHeap = createMinHeap(size);
for
(int i = 0; i < size; ++i)
minHeap->array[i]
= newNode(data[i], freq[i]);
minHeap->size
= size;
buildMinHeap(minHeap);
return
minHeap;
}
// The main function that builds Huffman tree
struct MinHeapNode* buildHuffmanTree(char data[], int
freq[], int size)
{
struct
MinHeapNode *left, *right, *top;
// Step
1: Create a min heap of capacity equal to size. Initially, there are
//
modes equal to size.
struct
MinHeap* minHeap = createAndBuildMinHeap(data, freq, size);
// Iterate
while size of heap doesn't become 1
while
(!isSizeOne(minHeap))
{
//
Step 2: Extract the two minimum freq items from min heap
left
= extractMin(minHeap);
right
= extractMin(minHeap);
//
Step 3: Create a new internal node with frequency equal to the
//
sum of the two nodes frequencies. Make the two extracted node as
//
left and right children of this new node. Add this node to the min heap
//
'$' is a special value for internal nodes, not used
top
= newNode('$', left->freq + right->freq);
top->left
= left;
top->right
= right;
insertMinHeap(minHeap,
top);
}
// Step
4: The remaining node is the root node and the tree is complete.
return
extractMin(minHeap);
}
// Prints huffman codes from the root of Huffman Tree. It
uses arr[] to
// store codes
void printCodes(struct MinHeapNode* root, int arr[], int
top)
{
//
Assign 0 to left edge and recur
if
(root->left)
{
arr[top]
= 0;
printCodes(root->left,
arr, top + 1);
}
//
Assign 1 to right edge and recur
if
(root->right)
{
arr[top]
= 1;
printCodes(root->right,
arr, top + 1);
}
// If
this is a leaf node, then it contains one of the input
//
characters, print the character and its code from arr[]
if
(isLeaf(root))
{
printf("%c:
", root->data);
printArr(arr,
top);
}
}
// The main function that builds a Huffman Tree and print
codes by traversing
// the built Huffman Tree
void HuffmanCodes(char data[], int freq[], int size)
{
// Construct Huffman Tree
struct MinHeapNode* root = buildHuffmanTree(data, freq, size);
// Print Huffman codes using the Huffman tree built above
int arr[MAX_TREE_HT], top = 0;
printCodes(root, arr, top);
}
// Driver program to test above functions
int main()
{
char
arr[] = {'a', 'b', 'c', 'd', 'e', 'f'};
int
freq[] = {5, 9, 12, 13, 16, 45};
int
size = sizeof(arr)/sizeof(arr[0]);
HuffmanCodes(arr,
freq, size);
return
0;
}
Output:
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