递归版本 ```void preorder(struct TreeNode*root,int*ret,int*returnSize) { if(root!=NULL){ ret[(*returnSize)++]=root->val; preorder(root->left, ret, returnSize); preorder(root->right, ret, returnSize); } } int* preorderTraversal(struct TreeNode* root, int* returnSize ) { int*ret=(int*)malloc(siz...