Validate Binary Search Tree
Link to leetcode problem definition
Given a binary tree, determine if it is a valid binary search tree (BST).
Assume a 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.
Example 1:
2
/ \
1 3
Input: [2,1,3] Output: true
Example 2:
5
/ \
1 4
/ \
3 6
Input: [5,1,4,null,null,3,6] Output: false
Explanation: The root node's value is 5 but its right child's value is 4.
class Solution {
public boolean isValidBST(TreeNode root) {
return isValid(root, null, null);
}
private boolean isValid(TreeNode node, Integer min, Integer max) {
if(node == null) {
return true;
}
if((min != null && node.val <= min) ||
(max != null && node.val >= max)) {
return false;
}
return isValid(node.left, min, node.val)
&& isValid(node.right, node.val, max);
}
}