388. Validate a BST
MediumBSTInorder
Print YES if the binary tree is a valid binary search tree (every left subtree < node < every right subtree), else NO.
Input format
Line 1: n (number of level-order entries) Line 2: the values in level order, -1 for a missing child
Output format
YES or NO
Example 1
Input
3 2 1 3
Output
YES
Example 2
Input
7 5 1 4 -1 -1 3 6
Output
NO
Constraints
1 ≤ nodes ≤ 10⁴ (values are positive)
Read input from standard input and print the answer to standard output. Your code is judged against 6 test cases, most of them hidden.
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