098_验证二叉搜索树

中等

Java

class Solution {
    public boolean isValidBST(TreeNode root) {
        return inSpread(root,(long)Integer.MIN_VALUE - 1,(long)Integer.MAX_VALUE + 1);
    }
    boolean inSpread(TreeNode node,long left,long right){
        if(node.val <= left || node.val >= right){
            return false;
        }
        if(node.left != null){
            if(!inSpread(node.left, left, node.val)) return false;
        }
        if(node.right != null){
            if(!inSpread(node.right, node.val, right)) return false;
        }
        return true;
    }
}

Python

class Solution:
    def isValidBST(self, root: Optional[TreeNode]) -> bool:
        def area(node,left=None,right=None):
            if node == None: return True
            elif(left is not None and left >= node.val) or (right is not None and right <= node.val):
                return False
            else:
                return area(node.left,left,node.val) and area(node.right,node.val,right)
            
        return area(root)

递归判断左右节点是否满足条件，传入参数为左右区间的值，小于等于left或大于等于right都是false