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C
Validate Binary Search TreeMedium1/3
24:38
Hint
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Problem
Clarifications

98. Validate Binary Search TreeMedium
Google
Amazon
Meta
Apple
Microsoft
+12
Given the root of a binary tree, determine if it is a valid binary search tree.
Every node in the left subtree must be smaller. Every node in the right subtree must be larger.
Examples
Example 1
Input: root = [8,3,10,1,6,null,14]
Output: true
Each node stays inside its inherited range.
Example 2
Input: root = [5,1,4,null,null,3,6]
Output: false
Constraints
1 <= nodes <= 10⁴
-2³¹ <= node.val <= 2³¹ - 1
Duplicate values are invalid.
Expected Complexity
TimeO(n)
SpaceO(h)

Validate Binary Search Treerange narrows
as we go down
low < node < high
8
3
10
1
6
14
root
(-inf, inf)
left
(-inf, 8)
right
(3, 8)
path: 8 -> 3 -> 6
return true
3 < 6 < 8
Let's draw the range each node is allowed to live inside.
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max sum of k = 3
current window
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5
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4
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5
l
r
drop 2, add 3
sum = 9
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