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  • 38: Validate Binary Search Tree

    /************************************************************************/
            /*       38:      Validate Binary Search Tree                            */
            /************************************************************************/
            /*
             *  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.

    confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.
             *
             * */
            
            
            /*
             * 二叉搜索树:
             *
             * */
            
            /**
             * Definition for binary tree
             * public class TreeNode {
             *     int val;
             *     TreeNode left;
             *     TreeNode right;
             *     TreeNode(int x) { val = x; }
             * }
             */
            
    /**1 : max(left nodes) < root&& min(right nodes)>root *******************************************/

    // 当 min(left node )>root || max(right nodes)<root 时 就肯定不是了

    public boolean isValidBST(TreeNode root)
            {
                return  validate(root,null,null);
            }
    
            boolean validate(TreeNode node, TreeNode tmin, TreeNode tmax) {
                if (node == null) return true;
                if (tmin != null && node.val <= tmin.val) return false;
                if (tmax != null && node.val >= tmax.val) return false;
                return validate(node.left, tmin, node) && validate(node.right, node, tmax);
            }
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  • 原文地址:https://www.cnblogs.com/theonemars/p/4254212.html
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