Binary Tree postorder Traversal

Problem description

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, cocould You Do It iteratively?

Solution

/** * 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) {        if( root == nullptr ) {            return { };        }            vector<int> result;        stack<TreeNode*> nodeStack;        nodeStack.push( root );                while( !nodeStack.empty() ) {            auto t = nodeStack.top();            nodeStack.pop();            if( t != nullptr ) {                result.push_back( t->val );                nodeStack.push( t->right );                nodeStack.push( t->left );            }        }        reverse( result.begin(), result.end() );        return result;    }};

Binary Tree postorder Traversal