test: migrate LeetCode 208 to new directory structure with tests

README.md

@@ -41,12 +41,12 @@ Each problem follows this structure:
 
 ## Solutions
 
-📊 **Statistics**: 87 problems solved (migrated to new structure)
+📊 **Statistics**: 88 problems solved (migrated to new structure)
 
 | Difficulty | Count |
 |------------|-------|
 | Easy       | 61    |
-| Medium     | 25    |
+| Medium     | 26    |
 | Hard       | 1     |
 
 ### Browse by Difficulty

docs/MEDIUM.md

@@ -1,6 +1,6 @@
 # Medium Problems
 
-Total: 25 problems solved
+Total: 26 problems solved
 
 ## Solutions
 
@@ -22,6 +22,7 @@ Total: 25 problems solved
 | 198 | [House Robber](https://leetcode.com/problems/house-robber/) | [solution.py](../problems/medium/house_robber_198/solution.py) | [test_solution.py](../problems/medium/house_robber_198/test_solution.py) |
 | 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/) | [solution.py](../problems/medium/number_of_islands_200/solution.py) | [test_solution.py](../problems/medium/number_of_islands_200/test_solution.py) |
 | 207 | [Course Schedule](https://leetcode.com/problems/course-schedule/) | [solution.py](../problems/medium/course_schedule_207/solution.py) | [test_solution.py](../problems/medium/course_schedule_207/test_solution.py) |
+| 208 | [Implement Trie (Prefix Tree)](https://leetcode.com/problems/implement-trie-prefix-tree/) | [solution.py](../problems/medium/implement_trie_prefix_tree_208/solution.py) | [test_solution.py](../problems/medium/implement_trie_prefix_tree_208/test_solution.py) |
 | 230 | [Kth Smallest Element in a BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/) | [solution.py](../problems/medium/kth_smallest_element_in_a_bst_230/solution.py) | [test_solution.py](../problems/medium/kth_smallest_element_in_a_bst_230/test_solution.py) |
 | 235 | [Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/) | [solution.py](../problems/medium/lowest_common_ancestor_of_a_binary_search_tree_235/solution.py) | [test_solution.py](../problems/medium/lowest_common_ancestor_of_a_binary_search_tree_235/test_solution.py) |
 | 236 | [Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) | [solution.py](../problems/medium/lowest_common_ancestor_of_a_binary_tree_236/solution.py) | [test_solution.py](../problems/medium/lowest_common_ancestor_of_a_binary_tree_236/test_solution.py) |

problems/medium/implement_trie_prefix_tree_208/solution.py

@@ -0,0 +1,55 @@
+# Tags: Hash Table, String, Design, Trie
+
+
+class Trie:
+
+    def __init__(self):
+        self.links: dict[str, Trie] = {}
+        self.is_end = False
+
+    def insert(self, word: str) -> None:
+        """
+        Time complexity : O(m), where m is the key(word) length.
+        In each iteration of the algorithm,
+        we either examine or create a node in the trie till we reach the end of the key.
+        This takes only m operations.
+
+        Space complexity : O(m).
+        In the worst case newly inserted key doesn't share
+        a prefix with the keys already inserted in the trie.
+        We have to add m new nodes, which takes us O(m) space.
+        """
+        curr = self
+        for c in word:
+            if c not in curr.links:
+                curr.links[c] = Trie()
+            curr = curr.links[c]
+        curr.is_end = True
+
+    def search(self, word: str) -> bool:
+        """
+        Time complexity : O(m)
+        In each step of the algorithm we search for the next key character.
+        In the worst case the algorithm performs m operations.
+
+        Space complexity : O(1)
+        """
+        curr = self
+        for c in word:
+            if c not in curr.links:
+                return False
+            curr = curr.links[c]
+        return curr.is_end
+
+    def starts_with(self, prefix: str) -> bool:
+        """
+        Time complexity : O(m)
+
+        Space complexity : O(1)
+        """
+        curr = self
+        for c in prefix:
+            if c not in curr.links:
+                return False
+            curr = curr.links[c]
+        return True

problems/medium/implement_trie_prefix_tree_208/test_solution.py

@@ -0,0 +1,38 @@
+from .solution import Trie
+
+
+class TestSolution:
+
+    def call(self, methods, params, expected):
+        results = []
+        obj = None
+        for method, param in zip(methods, params):
+            if method == "Trie":
+                obj = Trie()
+                results.append(None)
+            else:
+                result = getattr(obj, method)(*param)
+                results.append(result)
+        assert results == expected
+
+    def test_example_1(self):
+        """
+        Example 1:
+        Input: ["Trie", "insert", "search", "search", "starts_with", "insert", "search"]
+               [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
+        Output: [null, null, true, false, true, null, true]
+
+        Explanation:
+        Trie trie = new Trie();
+        trie.insert("apple");
+        trie.search("apple");   // return True
+        trie.search("app");     // return False
+        trie.starts_with("app"); // return True
+        trie.insert("app");
+        trie.search("app");     // return True
+        """
+        self.call(
+            ["Trie", "insert", "search", "search", "starts_with", "insert", "search"],
+            [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]],
+            [None, None, True, False, True, None, True],
+        )