【LeetCode】Binary Tree Preorder Traversal

地址：http://oj.leetcode.com/problems/binary-tree-preorder-traversal/

Binary Tree Preorder Traversal

 Total Accepted: 9880 Total Submissions: 28874My Submissions

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?

/** * 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) {        TreeNode *pnode;        stack<TreeNode*> stk;        vector<int> v;        stk.push(root);        if (root != NULL) while(!stk.empty()){            pnode = stk.top();            stk.pop();            v.push_back(pnode->val);            if (pnode->right != NULL)                stk.push(pnode->right);            if (pnode->left != NULL)                stk.push(pnode->left);        }        return v;    }};