leetcode226. Invert Binary Tree

交换二叉树两个节点

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
       if (root == NULL) {
            return NULL;
        }

        TreeNode* tempNode = root->left;
        root->left = root->right;
        root->right = tempNode;

        invertTree(root->left);
        invertTree(root->right);

        return root;
    }
};