399. Evaluate Division

from collections import deque
class Solution:
    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:
        self.graph = {}
        self.weight = {}
        
        for i in range(len(equations)):
            [u,v] = equations[i]
            
            if u in self.graph:
                self.graph[u].add(v)
            else:
                self.graph[u] = {v}
            
            if v in self.graph:
                self.graph[v].add(u)
            else:
                self.graph[v] = {u}
                
            self.weight[u+"-"+v] = values[i]
            self.weight[v+"-"+u] = 1/values[i]
        
        ans = []
        
        
        for query in queries:
            [x,y] = query
            
            if x not in self.graph:
                ans.append(-1)
                continue
            
            if x+"-"+y in self.weight:
                ans.append(self.weight[x+"-"+y])
                continue
            
            self.visited = set()
            
            ans.append(self.bfs(x,y,1) if x != y else 1.0)
        
        return ans
    
    
    def bfs(self, x: str,y: str,val: float) -> float:
        
        self.visited.add(x)
        
        q = deque([(val,x)])
        
        while q:
            (val,x) = q.popleft()
            
            if x+"-"+y in self.weight:
                return val*self.weight[x+"-"+y]
            
            for node in self.graph[x]:
                if node not in self.visited:
                    newval = val * self.weight[x+"-"+node]
                    q.append((newval,node))
                    self.visited.add(node)
        
        return -1