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  • 98. Validate Binary Search Tree

    package LeetCode_98
    
    import main.TreeNode
    
    /**
     * 98. Validate Binary Search Tree
     * https://leetcode.com/problems/validate-binary-search-tree/description/
     *
     * 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.
     * */
    class Solution {
        fun isValidBST(root: TreeNode?): Boolean {
            return help(root, null, null)
        }
    
        private fun help(root: TreeNode?, min: Int?, max: Int?): Boolean {
            if (root == null) {
                return true
            }
            if (min!=null && min >= root.`val` || max!=null && max <= root.`val`) {
                return false
            }
            return help(root.left, min, root.`val`) && help(root.right, root.`val`, max)
        }
    }
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  • 原文地址:https://www.cnblogs.com/johnnyzhao/p/13044180.html
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