数据结构2． 请编程实现哈夫曼树的构造，以及对该赫夫曼树的编码。

以下是Python代码实现哈夫曼树的构造和编码：

class Node:
    def __init__(self, value, freq):
        self.value = value
        self.freq = freq
        self.left = None
        self.right = None

def freq_dict(s):
    freq = {}
    for c in s:
        if c in freq:
            freq[c] += 1
        else:
            freq[c] = 1
    return freq

def huffman_tree(s):
    freq = freq_dict(s)
    nodes = [Node(k, v) for k, v in freq.items()]
    while len(nodes) > 1:
        nodes = sorted(nodes, key=lambda x: x.freq)
        left = nodes.pop(0)
        right = nodes.pop(0)
        parent = Node(left.value + right.value, left.freq + right.freq)
        parent.left = left
        parent.right = right
        nodes.append(parent)
    return nodes[0]

def huffman_encoding(s, root, code=''):
    if root.left is None and root.right is None:
        return {root.value: code}
    codes = {}
    codes.update(huffman_encoding(s, root.left, code + '0'))
    codes.update(huffman_encoding(s, root.right, code + '1'))
    return codes

s = 'hello world'
root = huffman_tree(s)
codes = huffman_encoding(s, root)
print(codes)

其中，我们定义了一个`Node`类来表示哈夫曼树的节点，包括节点的值（即字符）和频率，以及左右子节点。然后我们实现了`freq_dict`函数来统计字符串中每个字符出现的频率。接着，我们实现了`huffman_tree`函数来构造哈夫曼树。最后，我们实现了`huffman_encoding`函数来对哈夫曼树进行编码，返回每个字符对应的编码。