python

import decimal as dec class Symbolfr: def __init__(self, symbol, frequency): self.symbol = symbol self.frequency = frequency class Symbolbr: def __init__(self, symbol, low_board, high_board): self.symbol = symbol self.low_board = low_board self.high_board = high_board def _get_frequency(element): return element.frequency def get_symbols_boards(symbols_dict, symbol): for sym in symbols_dict: if sym.symbol == symbol: return sym.low_board, sym.high_board def get_symbols_frequency(user_string, precision=250): if precision <= 0: raise ValueError("Precision of encoding can not be less than zero") if len(user_string) == 0: raise ValueError("Received empty string") symbols_array = [] for ch in list(user_string): symbols_array.append(ch) symbols_array.sort() symbols_frequency = [] count = dec.Decimal(0) for ch_i in list(symbols_array): for ch_g in list(symbols_array): if ch_i == ch_g: count += dec.Decimal(1) is_exist = False for sym in symbols_frequency: if sym.symbol == ch_i: is_exist = True if not is_exist: symbols_frequency.append(Symbolfr(ch_i, count)) count = dec.Decimal(0) symbols_frequency.sort(key=_get_frequency, reverse=True) dec.getcontext().prec = precision return symbols_frequency def get_symbols_intervals(user_string, precision=250): if precision <= 0: raise ValueError("Precision of encoding can not be less than zero") vector_length = dec.Decimal(0) symbols_frequency = get_symbols_frequency(user_string, precision) for sym in symbols_frequency: if sym.frequency <= 0: raise ValueError("Frequency of symbol less than zero") vector_length += sym.frequency symbols_intervals = [] length = dec.Decimal(0) for element in symbols_frequency: low_board = length
high_board = low_board + element.frequency / vector_length length += element.frequency / vector_length symbols_intervals.append(Symbolbr(element.symbol, low_board, high_board)) return symbols_intervals def encode(user_string, precision=250): if precision <= 0: raise ValueError("Precision of encoding can not be less than zero") if len(user_string) == 0: raise ValueError("Received empty string") dec.getcontext().rounding = dec.ROUND_UP vector_length = dec.Decimal(0) symbols_frequency = get_symbols_frequency(user_string, precision) for sym in symbols_frequency: vector_length += sym.frequency symbols_intervals = get_symbols_intervals(user_string, precision) low_old = dec.Decimal(0) low_board = dec.Decimal(0) high_old = dec.Decimal(1) high_board = dec.Decimal(1) for ch in list(user_string): low, high = get_symbols_boards(symbols_intervals, ch) high_board = low_old + (high_old - low_old) * high low_board = low_old + (high_old - low_old) * low high_old = high_board low_old = low_board dec.getcontext().prec = precision return low_board, high_board def decode(symbols_frequency, code, precision_of_string=10): if precision_of_string <= 0: raise ValueError("Precision of string can not be less than zero") if code < 0 or code >= 1: raise ValueError("Incorrect code") vector_length = dec.Decimal(0) user_string = "" for sym in symbols_frequency: vector_length += sym.frequency count = int(sym.frequency) while count > 0: user_string += sym.symbol count -= 1 dec.getcontext().rounding = dec.ROUND_UP symbols_intervals = get_symbols_intervals(user_string) first_char = "" for sym in symbols_frequency: low, high = get_symbols_boards(symbols_intervals, sym.symbol) if low <= code <= high: first_char = sym.symbol user_string = [first_char] for i in range(0, precision_of_string - 1): low, high = get_symbols_boards(symbols_intervals, user_string[i]) code = (code - low) / (high - low) for sym in symbols_frequency: low, high = get_symbols_boards(symbols_intervals, sym.symbol) if low < code <= high: user_string.append(sym.symbol) result_string = "" for ch in user_string: result_string += ch return result_string