题目：

题解：

class Solution:
    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:
        # 构造图
        graph = defaultdict(list)
        for (u, v), value in zip(equations, values):
            graph[u].append((v, value))
            graph[v].append((u, 1 / value))

        def dfs(node, target, visited, acc_product):
            # 如果找到了目标节点，返回累积乘积
            if node == target:
                return acc_product
            # 标记当前节点为已访问
            visited.add(node)
            # 遍历当前节点的邻居
            for neighbor, value in graph[node]:
                if neighbor not in visited:
                    result = dfs(neighbor, target, visited, acc_product * value)
                    if result != -1:
                        return result
            return -1

        results = []
        for start, end in queries:
            if start in graph and end in graph:
                # 如果起点和终点都在图中，进行DFS
                results.append(dfs(start, end, set(), 1.0))
            else:
                # 否则，结果为-1
                results.append(-1.0)
        
        return results