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

apps/docs/content/(string)/211-design-add-and-search-words-data-structure.mdx

@@ -16,6 +16,43 @@ sidebar:
 - There will be at most 2 dots in `word` for search queries.
 - At most 10^4 calls will be made to addWord and search.
 
+## Approach
+
+```mermaid
+flowchart TD
+  subgraph state["state — root TrieNode; every node holds a children dict and an endOfWord flag"]
+    R["root"] --- C["... children[c] ..."] --- L["endOfWord = True — a word ends here"]
+  end
+  subgraph addWord["addWord(word)"]
+    A1["cur = root"] --> A2{"more c in word?"}
+    A2 -- yes --> A3{"c not in cur.children?"}
+    A3 -- yes --> A4["cur.children[c] = TrieNode()"]
+    A4 --> A5["cur = cur.children[c]"]
+    A3 -- no --> A5
+    A5 --> A2
+    A2 -- no --> A6["cur.endOfWord = True"]
+    A6 --> A7(["done"])
+  end
+  subgraph search["search(word)"]
+    S1["dfs(0, root) — match from index 0 at the root"] --> S2["cur = root"]
+    S2 --> S3{"more i in range(j, len(word))?"}
+    S3 -- no --> S4(["return cur.endOfWord"])
+    S3 -- yes --> S5["c = word[i]"]
+    S5 --> S6{"c == '.'?"}
+    S6 -- yes --> S7{"more child in cur.children.values()?"}
+    S7 -- yes --> S8{"dfs(i + 1, child)? — try the rest of the word from this child"}
+    S8 -- yes --> S9(["return True"])
+    S8 -- no --> S7
+    S7 -- no --> S10(["return False — no child matched the wildcard"])
+    S6 -- no --> S11{"c not in cur.children?"}
+    S11 -- yes --> S12(["return False"])
+    S11 -- no --> S13["cur = cur.children[c]"]
+    S13 --> S3
+  end
+  state --> addWord
+  state --> search
+```
+
 ## Solution
 
 ```py
@@ -63,3 +100,7 @@ class WordDictionary:
 # obj.addWord(word)
 # param_2 = obj.search(word)
 ```
+
+## Explanation
+
+<YouTube id="BTf05gs_8iU" title="Design Add and Search Words Data Structure - Leetcode 211 - Python" />