LintCode 翻转二叉树

题目描述：
翻转一棵二叉树

您在真实的面试中是否遇到过这个题？ Yes
样例
1 1
/ \ / \
2 3 => 3 2
/ \
4 4

思路分析：

交换左右子树。

ac代码：

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