docs(docs): add Approach diagrams and Explanation sections to LeetCode problem documentation

apps/docs/content/(tree)/199-binary-tree-right-side-view.mdx

@@ -29,6 +29,26 @@ sidebar:
 - The number of nodes in the tree is in the range [0, 100].
 - `-100 <= Node.val <= 100`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["rightSideView(root)"]) --> I["res = [], q = deque([root])"]
+  I --> W{"q non-empty?"}
+  W -- no --> E(["return res"])
+  W -- yes --> L["rightSide = None, qLen = len(q) — qLen freezes the current level's size"]
+  L --> F{"more i in range(qLen)?"}
+  F -- no --> V{"rightSide is not None?"}
+  V -- yes --> A["res.append(rightSide.val) — the last real node popped on this level is the rightmost"]
+  A --> W
+  V -- no --> W
+  F -- yes --> P["node = q.popleft()"]
+  P --> N{"node is not None?"}
+  N -- no --> F
+  N -- yes --> C["rightSide = node, q.append(node.left), q.append(node.right)"]
+  C --> F
+```
+
 ## Solution
 
 ```py
@@ -62,3 +82,7 @@ class Solution:
 
         return res
 ```
+
+## Explanation
+
+<YouTube id="d4zLyf32e3I" title="Binary Tree Right Side View - Breadth First Search - Leetcode 199" />