1 /**
2 * Definition for a binary tree node.
3 * struct TreeNode {
4 * int val;
5 * TreeNode *left;
6 * TreeNode *right;
7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
8 * };
9 */
10 class Solution {
11 public:
12 vector<int> preorderTraversal(TreeNode* root) {
13 vector<int> res;
14 if(root == NULL)
15 return res;
16 stack<TreeNode*> node;
17 node.push(root);
18 TreeNode *p, *cur;
19 p = root;
20 res.push_back(p->val);
21 while(!node.empty())
22 {
23 while(p->left != NULL)
24 {
25 p = p->left;
26 res.push_back(p->val);
27 node.push(p);
28 }
29 cur = node.top();
30 node.pop();
31 if(cur->right != NULL)
32 {
33 p = cur->right;
34 res.push_back(p->val);
35 node.push(p);
36 }
37 }
38 return res;
39 }
40 };
