Binary Search Tree (BST) is a data structure that is often used in coding interviews. It is a binary tree where all the nodes on the left side of a given node are smaller and all the nodes on the right side are larger. This makes it an efficient data structure for searching, inserting, and deleting elements.
Here are some common coding interview questions that can be solved using the Binary Search Tree pattern:
1. Validate Binary Search Tree
Given the root of a binary tree, determine if it is a valid binary search tree (BST).
Example:
Input: [2,1,3] Output: trueSolution:
class Solution:
def isValidBST(self, root: Optional[TreeNode]) -> bool:
def validate(node, low, high):
if not node:
return True
if not low < node.val < high:
return False
return (validate(node.left, low, node.val) and
validate(node.right, node.val, high))
return validate(root, float('-inf'), float('inf'))
2. Binary Tree Inorder Traversal
Given the root of a binary tree, return the inorder traversal of its nodes' values.
Example:
Input: [1,null,2,3] Output: [1,3,2]Solution:
class Solution:
def inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
def dfs(node, res):
if not node:
return
dfs(node.left, res)
res.append(node.val)
dfs(node.right, res)
res = []
dfs(root, res)
return res
3. Binary Tree Maximum Path Sum
Given a non-empty binary tree, find the maximum path sum.
Example:
Input: [-10,9,20,null,null,15,7] Output: 42 Explanation: The path with the maximum sum goes through nodes 15 -> 20 -> 7.
Solution:
class Solution:
def maxPathSum(self, root: Optional[TreeNode]) -> int:
def dfs(node):
if not node:
return 0
left_sum = max(dfs(node.left), 0)
right_sum = max(dfs(node.right), 0)
nonlocal max_sum
max_sum = max(max_sum, left_sum + node.val + right_sum)
return node.val + max(left_sum, right_sum)
max_sum = float('-inf')
dfs(root)
return max_sum
These are just a few examples of how the Binary Search Tree pattern can be used to solve coding interview questions. By understanding this pattern and practicing similar problems, you can improve your problem-solving skills and increase your chances of success in coding interviews.