递归-二叉搜索树-leetcode98验证二叉搜索树

//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
 
 思路：搜索树，左子树小于根节点，右子树大于根节点，根据这个特性去做
 
class Solution {
    public boolean isValidBST(TreeNode root) {
        return isValid(root,null,null);
    }

    boolean isValid(TreeNode root,TreeNode min,TreeNode max){
        if(root==null){
            return true ;
        }
        //节点的左子树只包含 小于 当前节点的数。
        if(min!=null && min.val>=root.val){
            return false;
        }
        //节点的右子树只包含 大于 当前节点的数。
        if(max!=null && max.val<=root.val){
            return false;
        }

        return isValid(root.left,min,root)&&isValid(root.right,root,max);
    }
}
//leetcode submit region end(Prohibit modification and deletion)