Binary Tree Preorder Traversal and Binary Tree Postorder Traversal

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].

 

c++版：

/**

 * 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) {  

        // IMPORTANT: Please reset any member data you declared, as  

        // the same Solution instance will be reused for each test case.  

        vector<int> result;  

        vector<int> left;  

        vector<int> right;  

          

        if(root == NULL) return result;  

        result.push_back(root->val);  

        left = preorderTraversal(root->left);  

        right = preorderTraversal(root->right);  

          

        if(left.size() != 0)  

            result.insert(result.end(), left.begin(), left.end());  

        if(right.size() != 0)  

            result.insert(result.end(), right.begin(), right.end());  

          

        return result;  

          

    }  

};

Binary Tree Postorder Traversal

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

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

   1

    \

     2

    /

   3

 

return [3,2,1].

C++版本：

/**

 * 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> postorderTraversal(TreeNode *root) {

        vector<int> ret;  

        dfs(root, ret);  

        return ret;  

    }  

  

    void dfs(TreeNode* root, vector<int>& ret)  

    {  

        if(NULL == root)  

            return ;  

        dfs(root->left, ret);  

        dfs(root->right, ret);  

        ret.push_back(root->val); 

    }     

    

};