Create huffman_coding.py

Author: abhisheks008

Greedy/Huffman Coding/huffman_coding.py

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+# Problem name: Huffman Coding
+# Approach: Greedy Method
+
+# -----------------------------------------------------------------------------------------------
+
+# Problem Statement: Huffman coding is a lossless data compression algorithm. 
+#                    The idea is to assign variable-length codes to input 
+#                    characters, lengths of the assigned codes are based on the 
+#                    frequencies of corresponding characters. The most frequent 
+#                    character gets the smallest code and the least frequent 
+#                    character gets the largest code.
+
+# -----------------------------------------------------------------------------------------------
+
+# Constraints:
+# chars[] -> set of characters/array of characters.
+# freq[] -> frequency of each of the characters in the given set.
+
+# -----------------------------------------------------------------------------------------------
+
+# importing the library named as heapq for the implementation of the huffman tree.
+import heapq
+
+# class node defined as the back bone of the node class 
+class node:
+    def __init__(self, freq, symbol, left=None, right=None):
+        # frequency of symbol
+        self.freq = freq
+ 
+        # symbol name (character)
+        self.symbol = symbol
+ 
+        # node left of current node
+        self.left = left
+ 
+        # node right of current node
+        self.right = right
+ 
+        # tree direction (0/1)
+        self.huff = ''
+         
+    def __lt__(self, nxt):
+        return self.freq < nxt.freq
+         
+ 
+# utility function to print huffman
+# codes for all symbols in the newly
+# created Huffman tree
+def printNodes(node, val=''):
+     
+    # huffman code for current node
+    newVal = val + str(node.huff)
+ 
+    # if node is not an edge node
+    # then traverse inside it
+    if(node.left):
+        printNodes(node.left, newVal)
+    if(node.right):
+        printNodes(node.right, newVal)
+ 
+        # if node is edge node then
+        # display its huffman code
+    if(not node.left and not node.right):
+        print("     {0}      ->        {1}".format(node.symbol, newVal))
+ 
+ 
+# characters for huffman tree
+chars = ['a', 'b', 'c', 'd', 'e', 'f']
+ 
+# frequency of characters
+freq = [ 5, 9, 12, 13, 16, 45]
+
+print ("-- Huffman Coding using Greedy Method --")
+print ()
+print ("Provided input for implementing the Huffman Tree...")
+print ("Characters        Frequency")
+print ("---------------------------")
+for k in range (0, len(chars)):
+    print ("     {0}      ->        {1}".format(chars[k],freq[k]))
+print ()
+
+ 
+# list containing unused nodes
+nodes = []
+ 
+# converting characters and frequencies
+# into huffman tree nodes
+for x in range(len(chars)):
+    heapq.heappush(nodes, node(freq[x], chars[x]))
+ 
+while len(nodes) > 1:
+     
+    # sort all the nodes in ascending order
+    # based on their frequency
+    left = heapq.heappop(nodes)
+    right = heapq.heappop(nodes)
+ 
+    # assign directional value to these nodes
+    left.huff = 0
+    right.huff = 1
+ 
+    # combine the 2 smallest nodes to create
+    # new node as their parent
+    newNode = node(left.freq+right.freq, left.symbol+right.symbol, left, right)
+ 
+    heapq.heappush(nodes, newNode)
+ 
+# Huffman Tree is ready!
+print ("Creating Huffman Tree...\n")
+print ("Your Huffman Tree is ready! Here you go...")
+print ()
+print ("Characters       Huffman Code")
+print ("-----------------------------")
+printNodes(nodes[0])
+
+
+# -----------------------------------------------------------------------------------------------
+
+# Output:
+# -- Huffman Coding using Greedy Method --
+
+# Provided input for implementing the Huffman Tree...
+# Characters        Frequency
+# ---------------------------
+#      a      ->        5
+#      b      ->        9
+#      c      ->        12
+#      d      ->        13
+#      e      ->        16
+#      f      ->        45
+
+# Creating Huffman Tree...
+
+# Your Huffman Tree is ready! Here you go...
+
+# Characters       Huffman Code
+# -----------------------------
+#      f      ->        0
+#      c      ->        100
+#      d      ->        101
+#      a      ->        1100
+#      b      ->        1101
+#      e      ->        111
+
+# -----------------------------------------------------------------------------------------------
+
+# Code contributed by, Abhishek Sharma, 2022
+
+# -----------------------------------------------------------------------------------------------