题目

399 除法求值

题目链接

官方题解

解题思路： 广度优先遍历

代码记录

class Solution:
    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:
        from collections import defaultdict
        self.link_path=defaultdict(list)
        self.link_value=defaultdict(float)
        for i in range(len(equations)):
            eq = equations[i]
            n1,n2 = eq
            if n2 not in self.link_path[n1]:
                self.link_path[n1].append(n2)
            if n1 not in self.link_path[n2]:
                self.link_path[n2].append(n1)
            self.link_value[(n1,n2)]=values[i]
            self.link_value[(n2,n1)]=1/values[i]
        def bfs(query):
            n_start,n_end = query
            res = 1.0
            if n_start==n_end and n_start in self.link_path:
                return res
            flag = False
            queue = [(n,self.link_value[(n_start,n)]) for n in self.link_path[n_start]]
            seen = {n_start:0}
            while queue:
                next_queue=[]
                for node,cur_value in queue:
                    if node==n_end:
                        flag = True
                        res = cur_value
                        break
                    elif node not in seen:
                        seen[node]=0
                        for next_node in self.link_path[node]:
                            if next_node not in seen:
                                next_queue.append((next_node,cur_value*self.link_value[(node,next_node)]))
                queue = next_queue
                if flag:
                    break
            res = res if flag else -1.0
            return res
        return [bfs(query) for query in queries]