#295 completed with a naive approach

Author: Hamid Gasmi

09-problems/lc_1483_kth_ancestor_of_tree_node.py

@@ -0,0 +1,57 @@
+"""
+    1. Problem Summary / Clarifications / TDD:
+        Parent :   -1   0   0   1   1   2   2
+        Node no:    0   1   2   3   4   5   6
+                 0
+               /   \
+              1     2
+             / \   / \
+            3   4 5   6
+
+"""
+class TreeAncestorNaive:
+    """
+    2. Inuition:
+        - Use a list to store all ancestors for each node: __ancestors
+        - The kth ancestor of node k will be stored in: __ancestors[node][k - 1]
+
+    3. Implementation:
+    4. Tests:
+
+    5. Complexity Analysis:
+        Time Complexity:
+            - Constructor: O(1)
+            - Get kth ancestor: O(n^2)
+                - Worst case (the tree looks like a linked list): O(n^2) = O(1 + 2 + 3 + ... + n) = O((n + 1) * n/2)
+                - Best case (the tree is balanced): O(logn^2) = O(1 + 2 + 3 + ... + logn) = O((logn + 1) * logn/2)
+        Space Complexity:
+            - Constructor: O(1)
+            - Get kth ancestor: O(n^2)
+                - Worst case (the tree looks like a linked list): O(n^2) = O(1 + 2 + 3 + ... + n) = O((n + 1) * n/2)
+                - Best case (the tree is balanced): O(logn^2) = O(1 + 2 + 3 + ... + logn) = O((logn + 1) * logn/2)
+
+        
+
+    """
+    def __init__(self, n: int, parent: List[int]):
+        
+        self.parent = parent
+        
+        self.__ancestors = {0:[]}
+    
+    def getKthAncestor(self, node: int, k: int) -> int:
+        if node not in self.__ancestors:
+            self.__find_all_ancestors(node)
+        
+        return self.__ancestors[node][k - 1] if k <= len(self.__ancestors[node]) else -1
+    
+    def __find_all_ancestors(self, node: int):
+        if node in self.__ancestors:
+            return
+        
+        parent = self.parent[node]
+        self.__ancestors[node] = [parent]
+        
+        self.__find_all_ancestors(parent)
+        self.__ancestors[node].extend(self.__ancestors[parent])
+