C solution
void travel(struct TreeNode root,int arr,int size){\n    if(root==NULL)\n        return;\n    arr[(size)++]=root->val;\n    travel(root->left,arr,size);\n    tr
void travel(struct TreeNode *root,int *arr,int *size){\n    if(root==NULL)\n        return;\n    arr[(*size)++]=root->val;\n    travel(root->left,arr,size);\n    travel(root->right,arr,size);\n}\nint* preorderTraversal(struct TreeNode* root, int* returnSize){\n    *returnSize=0;\n    int *arr=(int *)malloc(100*sizeof(int));\n    travel(root,arr,returnSize);\n    return arr;\n}
['Recursion', 'C']