Validate Binary Search Tree

描述

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.

分析

无

代码

// Validate Binary Search Tree
// 时间复杂度O(n)，空间复杂度O(\logn)
public class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValidBST(root, INT_MIN, INT_MAX);
    }

    bool isValidBST(TreeNode* root, int lower, int upper) {
        if (root == nullptr) return true;

        return root.val > lower && root.val < upper
                && isValidBST(root.left, lower, root.val)
                && isValidBST(root.right, root.val, upper);
    }
}

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