（1）书写代码，使之能够正确读取输入文本文件(test.{1, 2, 3}.txt)根据输入文本文件构造哈夫曼编码。把最优的哈夫曼编码写入输出文件{code.test.{1,2,3}.txt}。

以下是一个示例 Python 代码，可以读取输入文件并构造哈夫曼编码：

import heapq
from collections import defaultdict

# Define Node class for Huffman tree
class Node:
    def __init__(self, freq, char=None, left=None, right=None):
        self.freq = freq
        self.char = char
        self.left = left
        self.right = right

    def __lt__(self, other):
        return self.freq < other.freq


# Build Huffman tree
def build_huffman_tree(freq_dict):
    heap = []
    for key, value in freq_dict.items():
        heapq.heappush(heap, Node(value, key))

    while len(heap) > 1:
        left = heapq.heappop(heap)
        right = heapq.heappop(heap)
        parent = Node(left.freq + right.freq, left.char + right.char, left, right)
        heapq.heappush(heap, parent)

    return heap[0]


# Traverse Huffman tree and generate codes
def traverse_huffman_tree(node, code_dict, code=""):
    if node is None:
        return
    if node.char is not None:
        code_dict[node.char] = code
    traverse_huffman_tree(node.left, code_dict, code + "0")
    traverse_huffman_tree(node.right, code_dict, code + "1")


# Read input file and calculate character frequencies
def read_input_file(file_name):
    freq_dict = defaultdict(int)
    with open(file_name) as f:
        for line in f:
            for char in line.strip():
                freq_dict[char] += 1
    return freq_dict


# Write Huffman code to output file
def write_output_file(file_name, code_dict):
    with open(file_name, "w") as f:
        for key, value in code_dict.items():
            f.write(f"{key} {value}\n")


# Main function to build Huffman tree and generate codes
def main(input_file, output_file):
    freq_dict = read_input_file(input_file)
    huffman_tree = build_huffman_tree(freq_dict)
    code_dict = {}
    traverse_huffman_tree(huffman_tree, code_dict)
    write_output_file(output_file, code_dict)


# Test with sample input and output files
if __name__ == "__main__":
    main("test.txt", "code.test.txt")

使用该代码，可以读取名为 `test.txt` 的输入文件，计算字符频率，并构建哈夫曼树。然后，使用该哈夫曼树生成最优编码，并将其写入名为 `code.test.txt` 的输出文件中。

请注意，此示例代码仅适用于 ASCII 字符编码，并且没有处理 Unicode 字符。如果需要处理 Unicode 字符，则需要相应地修改代码。