LeetCode OJ - 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?

递归代码

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> preorderTraversal(TreeNode *root) {
vector<int> rslt;
preorder(root, rslt);
return rslt;
}

void preorder(TreeNode *root, vector<int> &rslt) {
if(root) {
rslt.push_back(root->val);
preorder(root->left, rslt);
preorder(root->right, rslt);
}
}
};