399

class Solution:
    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:

        g = defaultdict(list)
        for i, (a, b) in enumerate(equations):
            g[a].append((b, values[i]))
            g[b].append((a, 1/values[i]))

        def dfs(a, b):
            if a not in g or b not in g:
                return -1.0
            paths = dict()
            paths[a] = 1
            st = [a]
            while st:
                cur = st.pop()
                if cur == b:
                    return paths[b]
                for n, w in g[cur]:
                    if n not in paths:
                        paths[n] = paths[cur] * w
                        st.append(n)
            return -1.0

        res = []
        for a, b in queries:
            res.append(dfs(a, b))

        return res