536. Construct Binary Tree from String

You need to construct a binary tree from a string consisting of parenthesis and integers.

The whole input represents a binary tree. It contains an integer followed by zero, one or two pairs of parenthesis. The integer represents the root's value and a pair of parenthesis contains a child binary tree with the same structure.

You always start to construct the left child node of the parent first if it exists.

Example:

Input:

 "4(2(3)(1))(6(5))"
Output:

 return the tree root node representing the following tree:
       4
     /   \
    2     6
   / \   / 
  3   1 5   

Note:

1. There will only be '(' , ')' , '-' and '0' ~ '9' in the input string.
2. An empty tree is represented by "" instead of "()" .