Update 399_evaluate_division.md

Author: Joseph Luce

leetcode/medium/399_evaluate_division.md

@@ -1,6 +1,6 @@
 # 399. Evaluate Division
 
-## DFS Recursive Solution
+## DFS Solution
 - Runtime: O(N)
 - Space: O(N)
 - N = Number of unique nodes
@@ -42,3 +42,46 @@ class Solution:
             results.append(dfs(graph, start, end, set()))
         return results
 ```
+
+## BFS Solution
+- Runtime: O(N)
+- Space: O(N)
+- N = Number of unique nodes
+
+```
+from collections import deque
+from collections import defaultdict
+
+class Solution:
+    def calcEquation(self, equations: List[List[str]], values: List[float], queries: List[List[str]]) -> List[float]:
+        def create_graph():
+            graph = defaultdict(dict)
+            for eq, val in zip(equations, values):
+                start, end = eq
+                graph[start][end] = val
+                graph[end][start] = 1.0 / val
+            return graph
+        
+        def bfs(start, end, results):
+            queue = deque([(start, 1.0)])
+            visited = set()
+            while len(queue) != 0:
+                node, curr_prod = queue.pop()
+                if node not in graph:
+                    continue
+                if node == end:
+                    results.append(curr_prod)
+                    break
+                visited.add(node)
+                for neighbor, val in graph[node].items():
+                    if neighbor not in visited:
+                        queue.appendleft((neighbor, curr_prod * val))
+            else:
+                results.append(-1.0)
+
+        graph = create_graph()
+        results = list()
+        for start, end in queries:
+            bfs(start, end, results)
+        return results
+```