[Leetcode] Binary Tree Preorder Traversal

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

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

return [3,2,1].

Note:recursive solution is trivial, could do it iteratively?

Recursive implementation code

/***************************************************************** * @Author: Chu hing * @Date: 2015/2/23 18 : * @Status: Accepted * @Runtime: 4 ms******************************************************************/
     structtreenode{intVal    TreeNode *left;    TreeNode *right; TreeNode (intx): Val (x), left (null), right (null) {}};classSolution { Public: vector<int>Preordertraversal (TreeNode *root) { vector<int>Result Helper (root, result);returnResult }voidHelper (TreeNode *root, vector<int>& num) {if(Root)            {Num.push_back (root->val);            Helper (root->left, num);        Helper (root->right, num); }    }};

Non-recursive implementation code 1

/***************************************************************** * @Author: Chu hing * @Date: 2015/2/24 00 : Si * @Status: Accepted * @Runtime: 6 ms******************************************************************/
     classSolution { Public: vector<int>Preordertraversal (TreeNode *root) { vector<int>Result Stack<TreeNode*>Nodes TreeNode *p = root;if(p) {Nodes.push (P); while(!nodes.empty ())                {p = nodes.top ();                Nodes.pop (); Result.push_back (P->val);if(P->right)                {Nodes.push (p->right); }if(P->left)                {Nodes.push (p->left); }            }        }returnResult }};

Non-recursive implementation code 2

/***************************************************************** * @Author: Chu hing * @Date: 2015/2/24 01 : * @Status: Accepted * @Runtime: 4 ms******************************************************************/
     classSolution { Public: vector<int>Preordertraversal (TreeNode *root) { vector<int>Result Stack<TreeNode*>Nodes TreeNode *p = root; while(P! = NULL | |!nodes.empty ()) {if(P! = NULL) { while(P! = NULL)                    {Result.push_back (p->val);                    Nodes.push (P);                p = p->left; }            }Else{p = nodes.top ()->right;            Nodes.pop (); }        }returnResult }};

[Leetcode] Binary Tree Preorder Traversal