Add code for Huffman coding

huffman-coding.py

@@ -0,0 +1,77 @@
+from collections import Counter
+
+# function to find path of desired character
+def find_node(nodes, target_character):
+	# for each item in nodes
+    for index, item in enumerate(nodes):
+		# if item is desired character, return the path to it
+        if item == target_character:
+            return [str(index)]
+		# if the item is a list or tuple
+        if isinstance(item, (list, tuple)):
+			# run this function again to dig further into the nested items
+            path = find_node(item, target_character)
+			# if desired character is found, return its path
+            if path:
+                return [str(index)] + path
+	# if desired character not found, return empty list
+    return []
+
+# retrieve text to encode
+txt = input("Text: ")
+
+# create list of tuples in descending order of frequency: (character, frequency)
+info = Counter(txt).most_common()
+# change the list into ascending order
+info.reverse()
+# create list for character tuples
+nodes = []
+# create list for node usage frequencies
+frequencies = []
+
+# copy nodes and their usage frequencies to the dedicated lists
+for item in info:
+	nodes.append(item[0])
+	frequencies.append(item[1])
+
+# repeat until only one top-level node exists
+while len(nodes) > 1:
+	# combine two least frequent characters' nodes into a new tuple node, containing the old nodes (old_node_1, old_node_2)
+	new_node = (nodes[0], nodes[1])
+	# combine two least frequent characters' frequencies into a total frequency, to be used at the top level of the list of nodes
+	new_frequency = frequencies[0] + frequencies[1]
+	#  remove nodes that have been nested inside the new node
+	del nodes[0:2]
+	#  remove frequencies that have been summed and added to the new frequency
+	del frequencies[0:2]
+	# find index of last node with frequency below that of the new node
+	i = 0
+	# if there are more nodes to compare to
+	if (len(nodes) > 0):
+		# if the largest frequency is smaller than the new one, place the new node at the end of the list
+		if (frequencies[-1] < new_frequency):
+			i = -1
+		# else, if the first frequency is larger than the new one
+		elif not (frequencies[i] >= new_frequency):
+			# find the largest frequency that is smaller than the new one
+			while (frequencies[i] < new_frequency):
+				i += 1
+	# insert the new node in its rightful position, maintaining ascending order of frequency
+	nodes.insert(i, new_node)
+	# insert the new frequency in its rightful position, maintaining ascending order of frequency
+	frequencies.insert(i, new_frequency)
+
+# print all nodes
+print("Nodes: %s" % nodes)
+
+# encrypted text
+output = ""
+
+# for every character in the text to be encrypted
+for char in txt:
+	# find its path and add it to the encrypted text
+	output += "".join(find_node(nodes, char))
+
+# print encrypted message
+
+print("Encrypted message: %s" % output)