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Challenge of the Day

Today's Featured Challenge

Resets in 8h 24m

Intermediate JavaScript

50 points

Binary Search Tree Validator

Write a function to determine if a binary tree is a valid binary search tree. A valid BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the left and right subtrees must also be binary search trees.

Learning Objectives

Tree traversal, recursion, data structure validation

Time Estimate

30-45 minutes

Completed By

2,847 students

Solution Template

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */

function isValidBST(root) {
    // Your code here
    return true;
}

// Test cases
const tree1 = new TreeNode(2);
tree1.left = new TreeNode(1);
tree1.right = new TreeNode(3);

console.log(isValidBST(tree1)); // true

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solution.js

Code Editor

1  function twoSum(nums, target) {
2      const map = new Map();
3      
4      for (let i = 0; i < nums.length; i++) {
5          const complement = target - nums[i];
6          
7          if (map.has(complement)) {
8              return [map.get(complement), i];
9          }
10         
11         map.set(nums[i], i);
12     }
13     
14     return [];
15 }
16 
17 // Test cases
18 console.log(twoSum([2, 7, 11, 15], 9));

Test Case 1: Passed

Input: nums = [2,7,11,15], target = 9

Output: [0,1]

Expected: [0,1]

Test Case 2: Passed

Input: nums = [3,2,4], target = 6

Output: [1,2]

Expected: [1,2]

Test Case 3: Passed

Input: nums = [3,3], target = 6

Output: [0,1]

Expected: [0,1]

✓ All test cases passed!

Runtime: 68ms | Memory: 42.3MB

Line 18, Col 32 • UTF-8 • Spaces: 2

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