*************LeetCode 98 验证搜索二叉树

背下来

class Solution {
public boolean isValidBST(TreeNode root) {
return isBST(root, Long.MAX_VALUE, Long.MIN_VALUE);
}

private boolean isBST(TreeNode root, long maxValue, long minValue) {
if (root == null) return true;
if (root.val >= maxValue || root.val <= minValue) return false;
return isBST(root.left, root.val, minValue) && isBST(root.right, maxValue, root.val);
}
}