public static TreeNodeWithCount BuildTreeNode(TreeNode root)
{
if (root == null)
{
return(null);
}
TreeNodeWithCount node = new TreeNodeWithCount(root.val);
node.left = BuildTreeNode(root.left);
node.right = BuildTreeNode(root.right);
if (node.left != null)
{
node.count += node.left.count;
}
if (node.right != null)
{
node.count += node.right.count;
}
return(node);
}
public static int helper(TreeNodeWithCount node, int k)
{
if (node.left != null)
{
int cnt = node.left.count;
if (k <= cnt)
{
return(helper(node.left, k));
}
else if (k > cnt + 1)
{
return(helper(node.right, k - 1 - cnt));
}
return(node.val);
}
else
{
if (k == 1)
{
return(node.val);
}
return(helper(node.right, k - 1));
}
}
public int KthSmallest(TreeNode root, int k)
{
var tree = TreeNodeWithCount.BuildTreeNode(root);
return(TreeNodeWithCount.helper(tree, k));
}