leetcode[145]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].

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> postorderTraversal(TreeNode *root) {

        vector<int> res;

        if(root==NULL)return res;

        map<TreeNode *, int> smap;

        smap[root]=0;

        stack<TreeNode *> sta;

        sta.push(root);

        while(!sta.empty())

        {

            TreeNode *p=sta.top();

            if((!p->right&&!p->left)||smap.count(p->right)||smap.count(p->left))

            {

                res.push_back(p->val);

                smap[p]=1;

                sta.pop();

            }

            else

            {

               if(p->right&&!smap.count(p->right))

               {

                sta.push(p->right);

                smap[p->right]=0;

               }

               if(p->left&&!smap.count(p->left))

               {

                sta.push(p->left);

                smap[p->left]=0;

               }

            }

        }

        return res;

    }

/**

void postorder(vector<int> & res,TreeNode *root)

{

    if(root==NULL)return;

    postorder(res,root->left);

    postorder(res,root->right);

    res.push_back(root->val);

}

    vector<int> postorderTraversal(TreeNode *root) {

        vector<int> res;

        postorder(res,root);

        return res;

    }

*/

};