#define NULL ((void *)0)

//定义二叉树
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

//递归
void inorder(struct TreeNode* root, int* res, int* resSize) {
    if (!root)
        return;

    inorder(root->left, res, resSize);
    res[(*resSize)++] = root->val;
    inorder(root->right, res, resSize);
}

int* inorderTraversal(struct TreeNode* root, int* returnSize) {
    int* res = malloc(sizeof(int) * 501);
    *returnSize = 0;
    inorder(root, res, returnSize);
    return res;
}