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  • 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.

     

    /**
     * Definition for binary tree
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     * 详细解释
     * http://blog.csdn.net/sgbfblog/article/details/7771096
     */
    public class Solution {
        public boolean isValidBSTHelper(TreeNode root, int min, int max) {
            if (root==null) {
                return true;
            }
            return root.val > min && root.val < max && isValidBSTHelper(root.left, min, root.val) && isValidBSTHelper(root.right, root.val, max);
        }
        public boolean isValidBST(TreeNode root) {
            return isValidBSTHelper(root,Integer.MIN_VALUE, Integer.MAX_VALUE);
        }
    }
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  • 原文地址:https://www.cnblogs.com/23lalala/p/3506864.html
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