static void Main(string[] args)
{
TreeNode root = new TreeNode(5);
TreeNode n1 = new TreeNode(3);
TreeNode n2 = new TreeNode(6);
root.left = n1;
n1.left = n2;
//TreeNode n3 = new TreeNode(1);
//TreeNode n4 = new TreeNode(4);
//TreeNode n7 = new TreeNode(2);
//n1.left = n3;
//n1.right = n4;
//n3.right = n7;
Program p = new Program();
p.Flatten(root);
Console.WriteLine(root.val);
Console.ReadKey();
}
// return tail?
private TreeNode FlatTree(TreeNode node)
{
//base case - leaf
if (node.left == null && node.right == null) return node;
TreeNode rightTail = null;
if (node.right != null)
rightTail = FlatTree(node.right);
TreeNode leftTail = null;
if (node.left != null)
{
leftTail = FlatTree(node.left);
leftTail.right = node.right;
node.right = node.left;
node.left = null;
}
return rightTail == null ? leftTail : rightTail;
}
public void Flatten(TreeNode root)
{
if (root == null) return;
FlatTree(root);
}