226_Invert Binary Tree

反转二叉树，将每个节点的左节点和右节点交换

可以使用递归方法，先将交换函数在左节点和右节点递归下去，然后再交换左右节点

C:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
struct TreeNode* invertTree(struct TreeNode* root) {
    if(root == NULL)
    {
        return NULL;
    }
    struct TreeNode* leftNode = NULL;
    struct TreeNode* rightNode = NULL;
    if(root->left != NULL)
    {
        leftNode = invertTree(root->left);
    }
    if(root->right != NULL)
    {
        rightNode = invertTree(root->right);
    }
    root->left = rightNode;
    root->right = leftNode;
    
}