Find the maximum sum of path in a Binary Tree.
1. Use post order traveral or bottom up

                                            int maxSum(Node r){
                                                if(r != null){
                                                    int l = maxSum(r.left);
                                                    int r = maxSum(r.right);
                                                    return max(l, r) + r.data;
                                                }
                                                return 0;
                                            }