Tree PreOrder Traversal

Implement a PreOrder traversal of a tree. In this traversal the root node is visited first, then the left subtree and finally the right subtree.

Definition of a tree:

// Java
class TreeNode
{
public:
  int val;
  TreeNode left;
  TreeNode right;
  TreeNode(int x) {
    val = x;
    left = NULL; 
    right = NULL;
};

// C++
class TreeNode
{
public:
  int val;
  TreeNode *left;
  TreeNode *right;
  TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

Implement function PreOrder that prints in one line the vertices of the tree in order of PreOrder traversal. Separate the vertices with one space.

// Java
void PreOrder(TreeNode tree)

// C++
void PreOrder(TreeNode *tree)

Example

During the PreOrder traversal vertices will be printed in the next order: 4 2 1 3 10 9 16.