[lintcode easy]Invert Binary Tree

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    public void invertBinaryTree(TreeNode root) {
        // write your code here
        
        if(root==null) return;
        TreeNode left=root.left;
        TreeNode right=root.right;
        
        root.left=right;
        root.right=left;
        
        if(left!=null)
        {
            invertBinaryTree(left);
        }
        if(right!=null)
        {
            invertBinaryTree(right);
        }
        
        return;
    }
}