链接：
https://leetcode-cn.com/problems/binary-tree-preorder-traversal/description/
问题描述：
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
/**
* Return an array of size *returnSize.
* Note: The returned array must be malloced, assume caller calls free().
*/
int GetTreeSize(struct TreeNode* root)
{
if(root == NULL)
{
return 0;
}
else
{
return GetTreeSize(root->left) + GetTreeSize(root->right) + 1;
}
}
void _preorderTraversal(struct TreeNode* root, int* array,int* pIndex)
{
if(root == NULL)
return;
array[*pIndex] = root->val;
(*pIndex)++;
_preorderTraversal(root->left, array, pIndex);
_preorderTraversal(root->right, array, pIndex);
}
int* preorderTraversal(struct TreeNode* root, int* returnSize)
{
*returnSize = GetTreeSize(root);
int* array = (int*)malloc(*returnSize*sizeof(int));
int Index;
_preorderTraversal(root, array, &Index);
return array;
}
