/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */


struct TreeNode* invertTree(struct TreeNode* root){
    // 边界检查
    if (root == NULL) {
        return root;
    }

    // 动态分配一颗树
    struct TreeNode* pNode = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    // 判断是否申请成功
    if (pNode == NULL) {
        return NULL;
    }
    
    pNode->val = root->val;
    // 右子树变左子树
    pNode->left = invertTree(root->right);
    // 左子树变右子树
    pNode->right = invertTree(root->left);

    return pNode;
}