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question:# Question Context: You have been requested to develop a utility for encoding and decoding strings using a simple character shifting algorithm. This task will test your ability to implement string manipulation and basic encryption techniques. Problem Statement: Define two functions `encode_string(s: str, shift: int) -> str` and `decode_string(s: str, shift: int) -> str` that perform character shifting to encode and decode a string, respectively. The encoding shifts each character in the string `s` forward by `shift` positions in the alphabet, wrapping around if necessary. The decoding function reverses the process. Function Signatures: ```python def encode_string(s: str, shift: int) -> str: pass def decode_string(s: str, shift: int) -> str: pass ``` Input: * A string `s` comprised of lowercase English letters (1 ≤ `len(s)` ≤ 10^5). * An integer `shift` (0 ≤ `shift` < 26) - the number of positions each character in the string should be shifted. Output: * A string representing the encoded or decoded result. Constraints: 1. Handle edge cases where `s` is very small (e.g., `len(s) = 1`) or very large (e.g., `len(s) = 10^5`). 2. Ensure the `shift` value is within the specified range. 3. Optimize your solution for performance with respect to both encoding and decoding large strings. Performance Requirements: * Your solution should run efficiently for the maximum possible string length. Example: ```python assert encode_string("abc", 1) == "bcd" assert encode_string("xyz", 2) == "zab" assert decode_string("bcd", 1) == "abc" assert decode_string("zab", 2) == "xyz" assert encode_string("hello", 13) == "uryyb" assert decode_string("uryyb", 13) == "hello" ``` Additional Context: You might consider using modular arithmetic to simplify the character shifting process. The primary focus is to maintain simplicity and clarity in your algorithm while ensuring correctness and performance.
answer:def encode_string(s: str, shift: int) -> str: Encodes the input string `s` by shifting its characters `shift` positions forward in the alphabet. encoded_chars = [] for char in s: if char.isalpha(): new_pos = (ord(char) - ord('a') + shift) % 26 new_char = chr(new_pos + ord('a')) encoded_chars.append(new_char) else: # If there's a non-alphabet character, append as it is encoded_chars.append(char) return ''.join(encoded_chars) def decode_string(s: str, shift: int) -> str: Decodes the input string `s` by shifting its characters `shift` positions backward in the alphabet. decoded_chars = [] for char in s: if char.isalpha(): new_pos = (ord(char) - ord('a') - shift) % 26 new_char = chr(new_pos + ord('a')) decoded_chars.append(new_char) else: # If there's a non-alphabet character, append as it is decoded_chars.append(char) return ''.join(decoded_chars)
question:# Problem Description You are tasked with implementing a simplified version of a file synchronization tool that can track file changes and synchronize them between two directories. The goal is to identify new, modified, and deleted files in one directory and mirror those changes in another directory. # Function Specifications 1. **track_changes(src_dir: str, dest_dir: str) -> tuple**: Tracks changes between the source and destination directories. - **Input**: Two strings `src_dir` and `dest_dir` representing paths to the source and destination directories, respectively. - **Output**: A tuple containing three lists: - A list of new files in the source directory not present in the destination directory. - A list of modified files in the source directory that have a different checksum compared to corresponding files in the destination directory. - A list of files deleted from the source directory that are present in the destination directory. - **Behavior**: The function should recursively compare the contents of the two directories taking into account all files and subdirectories. 2. **synchronize(src_dir: str, dest_dir: str)**: Synchronizes the destination directory with the changes tracked in the source directory. - **Input**: Two strings `src_dir` and `dest_dir` representing paths to the source and destination directories, respectively. - **Output**: None - **Behavior**: The function should ensure that the destination directory reflects all changes identified by `track_changes` - new files should be copied, modified files should be updated, and deleted files should be removed. # Constraints - The directory paths will always be valid and accessible. - File checksums can be computed using the `hashlib` library (e.g., using `md5` hash). - Assume the directories do not contain any symbolic links or special file types. # Example ```python # Directory structure for example # src_dir/ # ├── file1.txt (content "Hello, World!") # ├── dir1 # │ └── file2.txt (content "Python is awesome") # # dest_dir/ # ├── file1.txt (content "Hello, World!") # └── file3.txt (content "Old file") # track_changes example new_files, modified_files, deleted_files = track_changes('src_dir', 'dest_dir') print(new_files) # ['dir1/file2.txt'] print(modified_files) # [] print(deleted_files) # ['file3.txt'] # synchronize example synchronize('src_dir', 'dest_dir') # After synchronization, dest_dir should have the following structure: # dest_dir/ # ├── file1.txt (content "Hello, World!") # ├── dir1 # │ └── file2.txt (content "Python is awesome") ``` # Requirements - Implement the `track_changes` function to correctly identify new, modified, and deleted files. - Implement the `synchronize` function to update the destination directory to match the source directory. - Ensure your implementation handles nested directories efficiently. - Provide sufficient error handling for common edge cases such as empty directories.
answer:import os import hashlib import shutil def calculate_checksum(file_path): Calculates the MD5 checksum of a file. hash_md5 = hashlib.md5() with open(file_path, "rb") as f: for chunk in iter(lambda: f.read(4096), b""): hash_md5.update(chunk) return hash_md5.hexdigest() def track_changes(src_dir, dest_dir): new_files = [] modified_files = [] deleted_files = [] src_files = {} dest_files = {} # Walk through the source directory to collect file paths and checksums for root, _, files in os.walk(src_dir): for file in files: file_path = os.path.join(root, file) relative_path = os.path.relpath(file_path, src_dir) src_files[relative_path] = calculate_checksum(file_path) # Walk through the destination directory to collect file paths and checksums for root, _, files in os.walk(dest_dir): for file in files: file_path = os.path.join(root, file) relative_path = os.path.relpath(file_path, dest_dir) dest_files[relative_path] = calculate_checksum(file_path) # Identify new files and modified files for relative_path, checksum in src_files.items(): if relative_path not in dest_files: new_files.append(relative_path) elif dest_files[relative_path] != checksum: modified_files.append(relative_path) # Identify deleted files for relative_path in dest_files.keys(): if relative_path not in src_files: deleted_files.append(relative_path) return new_files, modified_files, deleted_files def synchronize(src_dir, dest_dir): new_files, modified_files, deleted_files = track_changes(src_dir, dest_dir) # Add and update files for relative_path in new_files + modified_files: src_file_path = os.path.join(src_dir, relative_path) dest_file_path = os.path.join(dest_dir, relative_path) os.makedirs(os.path.dirname(dest_file_path), exist_ok=True) shutil.copy2(src_file_path, dest_file_path) # Delete files for relative_path in deleted_files: dest_file_path = os.path.join(dest_dir, relative_path) if os.path.exists(dest_file_path): os.remove(dest_file_path)
question:# Problem Statement You are given an array of integers, and your task is to move all the zeroes to the end of the array while maintaining the relative order of the non-zero elements. # Function to Implement ```python def move_zeroes(nums: list[int]) -> list[int]: Move all zeroes in the array to the end while maintaining the relative order of the non-zero elements. Parameters: nums (list[int]): The input list of integers. Returns: list[int]: The modified list with zeroes moved to the end. pass ``` # Example ```python nums = [0, 1, 0, 3, 12] result = move_zeroes(nums) # Output should be [1, 3, 12, 0, 0] nums = [0, 0, 1] result = move_zeroes(nums) # Output should be [1, 0, 0] ``` # Constraints 1. The input list will have at least one integer. 2. The list can have up to 10,000 integers. 3. Elements in the input array can be positive, negative, or zero. # Assumptions 1. The function should modify the input list in place. 2. The problem should be solved using constant space complexity. 3. The relative order of the non-zero elements must be preserved. # Performance Requirements Ensure that the solution handles large inputs efficiently, with a time complexity of O(n).
answer:def move_zeroes(nums: list[int]) -> list[int]: Move all zeroes in the array to the end while maintaining the relative order of the non-zero elements. Parameters: nums (list[int]): The input list of integers. Returns: list[int]: The modified list with zeroes moved to the end. last_non_zero_found_at = 0 # Move all the non-zero elements to the beginning of the array for current in range(len(nums)): if nums[current] != 0: nums[last_non_zero_found_at] = nums[current] last_non_zero_found_at += 1 # Fill the rest of the array with zeroes for i in range(last_non_zero_found_at, len(nums)): nums[i] = 0 return nums
question:# Dynamic Fibonacci Sequence Context The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding ones, often starting with 0 and 1. However, let's generalize this concept to support dynamic starting points and sequence lengths. Problem Design a function `dynamic_fibonacci(start1: int, start2: int, length: int) -> list` that takes three parameters: the first two starting numbers of the sequence and the total length of the desired sequence. The function should return a list containing the first `length` numbers of this generalized Fibonacci sequence. Input and Output Formats * **Input**: Three integers - the first number (`start1`), the second number (`start2`), and the total length of the desired sequence (`length`). * **Output**: A list of integers representing the sequence. Constraints * `start1` and `start2` are integers. * `length` is a positive integer (≥ 1). * If `length` is 1, only `start1` should be returned. Example ```python >>> dynamic_fibonacci(0, 1, 10) [0, 1, 1, 2, 3, 5, 8, 13, 21, 34] >>> dynamic_fibonacci(2, 3, 5) [2, 3, 5, 8, 13] >>> dynamic_fibonacci(4, 7, 1) [4] >>> dynamic_fibonacci(3, 3, 6) [3, 3, 6, 9, 15, 24] ``` # Requirements * The solution must efficiently generate the Fibonacci sequence based on given dynamic starting points. * Ensure the function correctly handles edge cases such as very small or very large sequence lengths.
answer:def dynamic_fibonacci(start1: int, start2: int, length: int) -> list: Generate a generalized Fibonacci sequence with specified starting points and length. Parameters: start1 (int): The first number in the sequence start2 (int): The second number in the sequence length (int): The total length of the desired sequence Returns: list: A list containing the first 'length' numbers of the sequence if length <= 0: return [] elif length == 1: return [start1] sequence = [start1, start2] for _ in range(2, length): next_value = sequence[-1] + sequence[-2] sequence.append(next_value) return sequence