[LeetCode]Invert Binary Tree

public class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return root;
        }
        TreeNode tmp1 = root.left;
        TreeNode tmp2 = root.right;
        root.right = invertTree(tmp1);
        root.left = invertTree(tmp2);
        return root;
    }
}