Pseudocode + big O for BFS (trekhleb#166)

Author: moshejs

src/algorithms/tree/breadth-first-search/README.md

@@ -8,6 +8,32 @@ nodes first, before moving to the next level neighbors.
 
 ![Algorithm Visualization](https://upload.wikimedia.org/wikipedia/commons/5/5d/Breadth-First-Search-Algorithm.gif)
 
+## Pseudocode
+
+    BFS(root)
+        Pre: root is the node of the BST
+        Post: the nodes in the BST have been visited in breadth first order
+        q ← queue
+        while root = ø
+            yield root.value
+            if root.left = ø
+                q.enqueue(root.left)
+            end if
+            if root.right = ø
+                q.enqueue(root.right)
+            end if
+            if !q.isEmpty()
+                root ← q.dequeue()
+            else
+                root ← ø
+            end if
+        end while
+    end BFS
+
+## Space and Time Complexity: 
+
+O(b<sup>d + 1</sup>) 
+
 ## References
 
 - [Wikipedia](https://en.wikipedia.org/wiki/Breadth-first_search)