struct stackEle{
        Node *n;
        int c;
        stackEle(Node *n,int c)
        {
            this->n = n;
            this->c = c;
        }
    };

    void postOrder(Node *root) {
        stack<stackEle> s;
        Node *cur = root;
        int c = 0;
        do{
            if(cur==NULL){
                if(s.empty())
                    break;
                else{
                    stackEle e = s.top();
                    s.pop();
                    cur = e.n;
                    c = e.c;
                }
            }else{
                if(c==0){
                    s.push(stackEle(cur,1));
                    cur = cur->left;
                    c = 0;
                }else if(c==1){
                  s.push(stackEle(cur, 2));
                  cur = cur->right;
                  c = 0;
                }else{
                    cout<<cur->data<<" ";
                    if(s.empty())
                        break;
                    else{
                      stackEle e = s.top();
                      s.pop();
                      cur = e.n;
                      c = e.c;
                    }
                }
            }
        }while(1);
    }