144_Binary Tree Preorder Traversal

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void PreOrder(TreeNode root, IList<int> path)
    {
        if(root != null)
        {
            path.Add(root.val);
            PreOrder(root.left, path);
            PreOrder(root.right, path);
        }
    }
        
    public IList<int> PreorderTraversal(TreeNode root) {
        List<int> result = new List<int>();
        PreOrder(root, result);
        return result;
    }
}