uk spelling: visualisation

backend/data/patterns/backtracking.yaml

@@ -84,7 +84,7 @@ visualization: |
   Eventually find: [1, 3, 0, 2] (queens at cols 1,3,0,2 for rows 0,1,2,3)
   ```
 
-  **Template visualization:**
+  **Template visualisation:**
 
   ```
   backtrack(state):

backend/data/patterns/dfs.yaml

@@ -67,7 +67,7 @@ visualization: |
   Order visited: A → B → D → F → E → C
   ```
 
-  **Recursion call stack visualization:**
+  **Recursion call stack visualisation:**
 
   ```
   dfs(A)

backend/data/questions/serialize-and-deserialize-binary-tree.yaml

@@ -145,7 +145,7 @@ explanation:
   key_takeaways:
     - "**Null markers are essential**: They encode the tree's *structure*, not just its values — this is what distinguishes serialization from simple traversal"
     - "**Preorder + nulls = unique tree**: Preorder traversal with null markers uniquely identifies any binary tree, enabling perfect reconstruction"
-    - "**BFS matches intuition**: Level-order serialization is often easier to visualize and debug since it matches how we draw trees"
+    - "**BFS matches intuition**: Level-order serialization is often easier to visualise and debug since it matches how we draw trees"
     - "**This pattern appears everywhere**: Serialization concepts apply to JSON parsing, protocol buffers, database storage, and network transmission of complex data structures"
 
   time_complexity: "O(n). Both serialization and deserialization visit each node exactly once, where `n` is the number of nodes in the tree."