[LeetCode]226. Invert Binary Tree

Easy

Invert a binary tree.

 4

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

0ms:

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