Problem Description
Given a binary tree, return the Postorder traversal of its nodes values..
Problem Constraints
1 <= number of nodes <= 105
Input Format
First and only argument is root node of the binary tree, A..
Output Format
Return an integer array denoting the Postorder traversal of the given binary tree..
/**
 /**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
vector<int> Solution::postorderTraversal(TreeNode* A) {
    stack<TreeNode*> post;
	post.push(A);
    vector<int>vec;
	
	stack<int> pout;
	while(!post.empty())
	{
		TreeNode *curr=post.top();
		post.pop();
		pout.push(curr->val);
		
		if(curr->left)
		{
			post.push(curr->left);
		}
		if(curr->right)
		{
			post.push(curr->right);
		}
	}
	while(!pout.empty())
	{
		vec.push_back(pout.top());
		pout.pop();
	}
    return vec;
}