Leetcode 144. Binary Tree Preorder Traversal

Given a binary tree, return the preorder traversal of its nodes‘ values.

For example:
Given binary tree {1,#,2,3},

   1
         2
    /
   3

return [1,2,3].

Note: Recursive solution is trivial, could you do it iteratively?

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解法：

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
vector<int> BiTPreTravesal; //这个地方有问题吗？
public:
vector<int> preorderTraversal(TreeNode* root) {
//1 定义一个迭代器，用来遍历vector中的元素
//vector<int> BiTPreTravesal;
// vevtor<int>::iterator iter;

//2 定义一个临时结点 pTempNode
TreeNode* pTempNode = root;


if( pTempNode != NULL )
{
BiTPreTravesal.push_back( pTempNode->val );

preorderTraversal(pTempNode->left);
preorderTraversal(pTempNode->right);

return BiTPreTravesal;
}

else
return BiTPreTravesal;


}
};