用python写出相关代码

为了完成这个实验任务，你可以使用Python编写一个程序来生成OBDD并将其转换为DOT格式。以下是一个简单的实现示例：

### 1. 安装依赖
首先，你需要安装`pydot`库来生成DOT文件。你可以使用以下命令安装它：

pip install pydot

### 2. 编写代码
下面是一个完整的Python程序，它可以读取布尔表达式，生成OBDD，并输出DOT格式的字符串。

import re
from collections import defaultdict

class Node:
    def __init__(self, var, low=None, high=None):
        self.var = var
        self.low = low
        self.high = low if low is None else high

def build_bdd(expr, vars_order):
    # Simplify the expression using De Morgan's laws and double negation
    expr = simplify_expr(expr)
    
    # Create a cache to store already computed nodes
    cache = {}
    
    def bdd_rec(expr, level=0):
        if expr in ['0', '1']:
            return Node(None, None, None) if expr == '0' else Node(None, None, None)
        
        if (expr, level) in cache:
            return cache[(expr, level)]
        
        var = vars_order[level]
        then_part = re.sub(r'\b' + var + r'\b', '1', expr)
        else_part = re.sub(r'\b' + var + r'\b', '0', expr)
        
        then_node = bdd_rec(then_part, level + 1)
        else_node = bdd_rec(else_part, level + 1)
        
        node = Node(var, else_node, then_node)
        cache[(expr, level)] = node
        
        return node
    
    root = bdd_rec(expr)
    return root

def simplify_expr(expr):
    while True:
        new_expr = expr.replace('not not ', '')
        new_expr = new_expr.replace('and not', 'or')
        new_expr = new_expr.replace('or not', 'and')
        if new_expr == expr:
            break
        expr = new_expr
    return expr

def generate_dot(node):
    dot = "digraph OBDD {\n"
    dot += "node [shape=circle];\n"
    dot += "edge [label=\"0\" color=red];\n"
    dot += "edge [label=\"1\" color=blue];\n"
    
    visited = set()
    stack = [(node, "root")]
    
    while stack:
        n, name = stack.pop()
        if id(n) in visited:
            continue
        visited.add(id(n))
        
        if n.var is None:
            label = "1" if n.high is None else "0"
            dot += f"{name} [label={label}, shape=square];\n"
        else:
            dot += f"{name} [label={n.var}];\n"
            if n.low is not None:
                low_name = f"{id(n.low)}"
                dot += f"{name} -> {low_name} [style=dashed];\n"
                stack.append((n.low, low_name))
            if n.high is not None:
                high_name = f"{id(n.high)}"
                dot += f"{name} -> {high_name};\n"
                stack.append((n.high, high_name))
    
    dot += "}\n"
    return dot

if __name__ == "__main__":
    expr = input("Enter a Boolean expression: ")
    vars_order = list(input("Enter the order of variables: "))
    
    bdd_root = build_bdd(expr, vars_order)
    dot_code = generate_dot(bdd_root)
    
    with open("output.dot", "w") as f:
        f.write(dot_code)
    
    print("OBDD DOT code has been written to output.dot")

### 3. 运行程序
1. 将上述代码保存为 `obdd_generator.py`。
2. 在终端或命令行中运行以下命令：

   python obdd_generator.py

3. 按照提示输入布尔表达式和变量顺序。

### 4. 可视化OBDD
1. 使用Graphviz在线工具（如 [Graphviz Online](https://dreampuf.github.io/GraphvizOnline/)）或本地安装的Graphviz工具。
2. 将生成的 `output.dot` 文件内容粘贴到Graphviz工具中，即可生成OBDD的图形表示。

希望这个示例对你有所帮助！如果你有任何问题，请随时提问。