Merge pull request #1541 from ivanpenaloza/february07

adding algo

Author: ivanpenaloza

src/my_project/interviews/top_150_questions_round_22/ex_69_construct_tree_from_preorder_inorder_traversal.py

@@ -0,0 +1,39 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+        # Create a hashmap for quick lookup of indices in inorder
+        inorder_map = {val: idx for idx, val in enumerate(inorder)}
+        self.preorder_idx = 0
+        
+        def build(left: int, right: int) -> Optional[TreeNode]:
+            # Base case: no elements to construct the tree
+            if left > right:
+                return None
+            
+            # Pick the current root from preorder
+            root_val = preorder[self.preorder_idx]
+            root = TreeNode(root_val)
+            
+            # Move to the next element in preorder
+            self.preorder_idx += 1
+            
+            # Find the index of root in inorder to split left and right subtrees
+            inorder_idx = inorder_map[root_val]
+            
+            # Build left subtree (all elements before root in inorder)
+            root.left = build(left, inorder_idx - 1)
+            
+            # Build right subtree (all elements after root in inorder)
+            root.right = build(inorder_idx + 1, right)
+            
+            return root
+        
+        return build(0, len(inorder) - 1)

src/my_project/interviews/top_150_questions_round_22/ex_70_construct_tree_from_preorder_postorder_traversal.py

@@ -0,0 +1,40 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+    def buildTree(self, inorder: List[int], postorder: List[int]) -> Optional[TreeNode]:
+        # Create a hashmap for quick lookup of indices in inorder
+        inorder_map = {val: idx for idx, val in enumerate(inorder)}
+        self.postorder_idx = len(postorder) - 1
+        
+        def build(left: int, right: int) -> Optional[TreeNode]:
+            # Base case: no elements to construct the tree
+            if left > right:
+                return None
+            
+            # Pick the current root from postorder (from end)
+            root_val = postorder[self.postorder_idx]
+            root = TreeNode(root_val)
+            
+            # Move to the previous element in postorder
+            self.postorder_idx -= 1
+            
+            # Find the index of root in inorder to split left and right subtrees
+            inorder_idx = inorder_map[root_val]
+            
+            # Build right subtree first (postorder: left → right → root)
+            # So when we go backwards, we process root → right → left
+            root.right = build(inorder_idx + 1, right)
+            
+            # Build left subtree
+            root.left = build(left, inorder_idx - 1)
+            
+            return root
+        
+        return build(0, len(inorder) - 1)

src/my_project/interviews_typescript/top_150_questions_round_1/ex_69_construct_tree_from_preorder_inorder_traversal.ts

@@ -0,0 +1,37 @@
+import { TreeNode } from './TreeNode';         
+
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+    // Create a hashmap for quick lookup of indices in inorder
+    const inorderMap = new Map<number, number>();
+    inorder.forEach((val, idx) => inorderMap.set(val, idx));
+    
+    let preorderIdx = 0;
+    
+    function build(left: number, right: number): TreeNode | null {
+        // Base case: no elements to construct the tree
+        if (left > right) {
+            return null;
+        }
+        
+        // Pick the current root from preorder
+        const rootVal = preorder[preorderIdx];
+        const root = new TreeNode(rootVal);
+        
+        // Move to the next element in preorder
+        preorderIdx++;
+        
+        // Find the index of root in inorder to split left and right subtrees
+        const inorderIdx = inorderMap.get(rootVal)!;
+        
+        // Build left subtree (all elements before root in inorder)
+        root.left = build(left, inorderIdx - 1);
+        
+        // Build right subtree (all elements after root in inorder)
+        root.right = build(inorderIdx + 1, right);
+        
+        return root;
+    }
+    
+    return build(0, inorder.length - 1);
+}
+

src/my_project/interviews_typescript/top_150_questions_round_1/ex_70_construct_tree_from_preorder_postorder_traversal.ts

@@ -0,0 +1,38 @@
+import { TreeNode } from './TreeNode'; 
+
+function buildTree(inorder: number[], postorder: number[]): TreeNode | null {
+    // Create a hashmap for quick lookup of indices in inorder
+    const inorderMap = new Map<number, number>();
+    inorder.forEach((val, idx) => inorderMap.set(val, idx));
+    
+    let postorderIdx = postorder.length - 1;
+    
+    function build(left: number, right: number): TreeNode | null {
+        // Base case: no elements to construct the tree
+        if (left > right) {
+            return null;
+        }
+        
+        // Pick the current root from postorder (from end)
+        const rootVal = postorder[postorderIdx];
+        const root = new TreeNode(rootVal);
+        
+        // Move to the previous element in postorder
+        postorderIdx--;
+        
+        // Find the index of root in inorder to split left and right subtrees
+        const inorderIdx = inorderMap.get(rootVal)!;
+        
+        // Build right subtree first (postorder: left → right → root)
+        // So when we go backwards, we process root → right → left
+        root.right = build(inorderIdx + 1, right);
+        
+        // Build left subtree
+        root.left = build(left, inorderIdx - 1);
+        
+        return root;
+    }
+    
+    return build(0, inorder.length - 1);
+}
+

tests/test_150_questions_round_22/test_69_construct_tree_from_preorder_inorder_traversal_round_22.py

@@ -0,0 +1,53 @@
+import unittest
+from typing import Optional, List
+from src.my_project.interviews.top_150_questions_round_22\
+.ex_69_construct_tree_from_preorder_inorder_traversal import Solution, TreeNode
+
+class ConstructTreeFromPreorderInorderTraversalTestCase(unittest.TestCase):
+
+    def tree_to_list(self, root: Optional[TreeNode]) -> List[Optional[int]]:
+        """Convert tree to level-order list representation with None for missing nodes."""
+        if not root:
+            return []
+        
+        result = []
+        queue = [root]
+        
+        while queue:
+            node = queue.pop(0)
+            if node:
+                result.append(node.val)
+                queue.append(node.left)
+                queue.append(node.right)
+            else:
+                result.append(None)
+        
+        # Remove trailing None values
+        while result and result[-1] is None:
+            result.pop()
+        
+        return result
+
+    def test_example_1(self):
+        """
+        Input: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
+        Output: [3,9,20,null,null,15,7]
+        """
+        solution = Solution()
+        preorder = [3, 9, 20, 15, 7]
+        inorder = [9, 3, 15, 20, 7]
+        output = solution.buildTree(preorder, inorder)
+        expected = [3, 9, 20, None, None, 15, 7]
+        self.assertEqual(self.tree_to_list(output), expected)
+
+    def test_example_2(self):
+        """
+        Input: preorder = [-1], inorder = [-1]
+        Output: [-1]
+        """
+        solution = Solution()
+        preorder = [-1]
+        inorder = [-1]
+        output = solution.buildTree(preorder, inorder)
+        expected = [-1]
+        self.assertEqual(self.tree_to_list(output), expected)

tests/test_150_questions_round_22/test_70_construct_tree_from_preorder_postorder_traversal_round_22.py

@@ -0,0 +1,53 @@
+import unittest
+from typing import Optional, List
+from src.my_project.interviews.top_150_questions_round_22\
+.ex_70_construct_tree_from_preorder_postorder_traversal import Solution, TreeNode
+
+class ConstructTreeFromPreorderPostorderTestCase(unittest.TestCase):
+
+    def tree_to_list(self, root: Optional[TreeNode]) -> List[Optional[int]]:
+        """Convert tree to level-order list representation with None for missing nodes."""
+        if not root:
+            return []
+        
+        result = []
+        queue = [root]
+        
+        while queue:
+            node = queue.pop(0)
+            if node:
+                result.append(node.val)
+                queue.append(node.left)
+                queue.append(node.right)
+            else:
+                result.append(None)
+        
+        # Remove trailing None values
+        while result and result[-1] is None:
+            result.pop()
+        
+        return result
+
+    def test_example_1(self):
+        """
+        Input: inorder = [9,3,15,20,7], postorder = [9,15,7,20,3]
+        Output: [3,9,20,null,null,15,7]
+        """
+        solution = Solution()
+        inorder = [9, 3, 15, 20, 7]
+        postorder = [9, 15, 7, 20, 3]
+        output = solution.buildTree(inorder, postorder)
+        expected = [3, 9, 20, None, None, 15, 7]
+        self.assertEqual(self.tree_to_list(output), expected)
+
+    def test_example_2(self):
+        """
+        Input: inorder = [-1], postorder = [-1]
+        Output: [-1]
+        """
+        solution = Solution()
+        inorder = [-1]
+        postorder = [-1]
+        output = solution.buildTree(inorder, postorder)
+        expected = [-1]
+        self.assertEqual(self.tree_to_list(output), expected)