226.Invert Binary Tree

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

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

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
/*
* 递归遍历整个树的每一个节点
* 并且若该节点不为空，则让其左右子节点互换
*/
public TreeNode invertTree(TreeNode root) {

if(root == null)
return root;

TreeNode transit = root.left;
root.left = root.right;
root.right = transit;

if(root.left != null)
root.left = invertTree(root.left);
if(root.right != null)
root.right = invertTree(root.right);
return root;
}
}