144.Binary Tree Preorder Traversal

/**
* 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 {
public:
vector<int> preorderTraversal(TreeNode* root)
{
vector<int> v;
TreeNode *temp = root;
if (!root) return v;
stack<TreeNode *> s;
s.push(root);
while (!s.empty())
{
temp = s.top();
v.push_back(temp->val);
s.pop();
if (temp->right) s.push(temp->right);
if (temp->left)	s.push(temp->left);
}
return v;
}
};