• https://leetcode.com/problems/validate-binary-search-tree/
• 98. Validate Binary Search Tree

JavaScript 解答

var isValidBST = function(root) {
    return helper(root, null, null);
}

function helper(node, low, high) {
    if (node === null) return true;
    const val = node.val;
    if ((low !== null && val <= low) || (high !== null && val >= high)) 
        return false;
    return helper(node.right, val, high) && helper(node.left, low, val);
}

Ruby 解答

def is_valid_bst(root)
    return is_valid(root,nil,nil)
end

def is_valid(root, min, max)
    return !root || ((!max || root.val< max) && (! min || root.val >min) && is_valid(root.left,min,root.val) && is_valid(root.right,root.val,max))
end