invert binary tree

Invert a binary tree.

     4
   /   
  2     7
 /    / 
1   3 6   9

to

     4
   /   
  7     2
 /    / 
9   6 3   1

最开始想到了递归

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null){
            return root;
        }
        TreeNode temp;
        temp = root.left;
        root.left = root.right;
        root.right = temp;

        root.left = invertTree(root.left);
        root.right = invertTree(root.right);
        return root;
    }
}

经过推算代码应该是通过的。

  2
 /    
3   1

要invert这课子树，其实是应该更换2节点内的指针，将他指向3节点和1节点的指针交换

官方答案：

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null){
            return root;
        }            
        TreeNode left = invertTree(root.left);
        TreeNode right = invertTree(root.right);
        root.right = left;
        root.left = right;
        return root;
    }
}