Evaluate Division

// LC: Evaluate Division

class Solution:
    def DFS(self, src, des, visited, graph, curr):
        if (src not in graph) or (des not in graph) or (src in visited):
            return -1
        
        if src == des:
            return curr
        
        visited.add(src)
        
        for nbr in graph[src]:
            prod = self.DFS(nbr[0], des, visited, graph, curr * nbr[1])
            
            if prod != -1:
                return prod
        
        return -1
            
    
    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:
        
        graph = defaultdict(list)
        for i in range(len(values)):
            u, v = equations[i]  # u / v
            val = values[i]
            
            graph[u].append((v, val))
            graph[v].append((u, 1 / val))
            

        ans = []
        
        # Each query is independent
        for q in queries:
            src, des = q[0], q[1]
            visited = set()
            
            ok = self.DFS(src, des, visited, graph, 1.0)
            
            ans.append(ok)
        
        return ans