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93 lines
2.7 KiB
Python
93 lines
2.7 KiB
Python
from __future__ import annotations
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import sys
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class Letter:
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def __init__(self, letter: str, freq: int):
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self.letter: str = letter
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self.freq: int = freq
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self.bitstring: dict[str, str] = {}
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def __repr__(self) -> str:
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return f"{self.letter}:{self.freq}"
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class TreeNode:
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def __init__(self, freq: int, left: Letter | TreeNode, right: Letter | TreeNode):
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self.freq: int = freq
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self.left: Letter | TreeNode = left
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self.right: Letter | TreeNode = right
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def parse_file(file_path: str) -> list[Letter]:
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"""
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Read the file and build a dict of all letters and their
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frequencies, then convert the dict into a list of Letters.
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"""
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chars: dict[str, int] = {}
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with open(file_path) as f:
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while True:
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c = f.read(1)
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if not c:
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break
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chars[c] = chars[c] + 1 if c in chars else 1
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return sorted((Letter(c, f) for c, f in chars.items()), key=lambda x: x.freq)
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def build_tree(letters: list[Letter]) -> Letter | TreeNode:
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"""
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Run through the list of Letters and build the min heap
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for the Huffman Tree.
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"""
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response: list[Letter | TreeNode] = letters # type: ignore
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while len(response) > 1:
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left = response.pop(0)
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right = response.pop(0)
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total_freq = left.freq + right.freq
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node = TreeNode(total_freq, left, right)
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response.append(node)
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response.sort(key=lambda x: x.freq)
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return response[0]
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def traverse_tree(root: Letter | TreeNode, bitstring: str) -> list[Letter]:
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"""
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Recursively traverse the Huffman Tree to set each
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Letter's bitstring dictionary, and return the list of Letters
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"""
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if isinstance(root, Letter):
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root.bitstring[root.letter] = bitstring
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return [root]
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treenode: TreeNode = root # type: ignore
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letters = []
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letters += traverse_tree(treenode.left, bitstring + "0")
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letters += traverse_tree(treenode.right, bitstring + "1")
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return letters
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def huffman(file_path: str) -> None:
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"""
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Parse the file, build the tree, then run through the file
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again, using the letters dictionary to find and print out the
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bitstring for each letter.
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"""
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letters_list = parse_file(file_path)
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root = build_tree(letters_list)
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letters = {
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k: v for letter in traverse_tree(root, "") for k, v in letter.bitstring.items()
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}
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print(f"Huffman Coding of {file_path}: ")
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with open(file_path) as f:
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while True:
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c = f.read(1)
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if not c:
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break
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print(letters[c], end=" ")
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print()
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if __name__ == "__main__":
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# pass the file path to the huffman function
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huffman(sys.argv[1])
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