题解 | #判断是不是二叉搜索树#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {

    private Integer curMax = null;
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    public boolean isValidBST (TreeNode root) {
        // write code here
        try {
            inorder(root);
        } catch (RuntimeException e) {
            return false;
        }
        return true;
    }

    private void inorder(TreeNode root) {
        if (root == null) {
            return;
        }

        inorder(root.left);
        if (curMax != null) {
            if (root.val < curMax) {
                throw new RuntimeException();
            }
            curMax = root.val;
        } else {
            curMax = root.val;
        }
        inorder(root.right);
    }
}