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CheckValidBST.cpp
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CheckValidBST.cpp
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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
bool isValidBST(TreeNode* root) {
// Account for empty tree
if (root == NULL)
return true;
// Use smallest and largest int values to start to account for root node
return is_valid_BST_helper(root, INT_MIN, INT_MAX);
}
bool is_valid_BST_helper(TreeNode* root, long min, long max)
{
// Reached a leaf node
if (root == NULL)
return true;
// If it breaks the rules
if (root->val < min || root->val > max)
return false;
// Otherwise, recurse by visiting both children
// Here we do not want to allow equal values so we subtract and add 1 respectively
if (!is_valid_BST_helper(root->left, min, (long) root->val - 1) ||
!is_valid_BST_helper(root->right, (long) root->val + 1, max))
return false;
// Catch-all
return true;
}
};