LeetCode -- Invert Binary Tree

题目描述：
Invert a binary tree.


     4
   /   \
  2     7
 / \   / \
1   3 6   9
to
     4
   /   \
  7     2
 / \   / \
9   6 3   1




就是把一棵二叉树进行反转。


思路：
本题的实现比较直接：后续遍历，交换节点。


实现代码：

/**
 * 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 TreeNode InvertTree(TreeNode root) 
    {
        
        Travel(ref root);
    	return root;
    }


private void Travel(ref TreeNode current)
{
	if(current == null || current.left == null && current.right == null){
		return;
	}
	
	Travel(ref current.left);
	Travel(ref current.right);
	Swap(ref current);
}




private void Swap(ref TreeNode n)
{
	var tmp = n.left;
	n.left = n.right;
	n.right = tmp;
}
}