7-3 Postfix Expression (25分)

7-3 Postfix Expression (25分)
Given a syntax tree (binary), you are supposed to output the corresponding postfix expression, with parentheses reflecting the precedences of the operators.

Input Specification:
Each input file contains one test case. For each case, the first line gives a positive integer N (≤ 20) which is the total number of nodes in the syntax tree. Then N lines follow, each gives the information of a node (the i-th line corresponds to the i-th node) in the format:

data left_child right_child
where data is a string of no more than 10 characters, left_child and right_child are the indices of this node's left and right children, respectively. The nodes are indexed from 1 to N. The NULL link is represented by −1. The figures 1 and 2 correspond to the samples 1 and 2, respectively.

Output Specification:
For each case, print in a line the postfix expression, with parentheses reflecting the precedences of the operators.There must be no space between any symbols.

Sample Input 1:
8

• 8 7
  a -1 -1
• 4 1

• 2 5
  b -1 -1
  d -1 -1

• -1 6
  c -1 -1
  Sample Output 1:
  (((a)(b)+)((c)(-(d))))
  Sample Input 2:
  8
  2.35 -1 -1

• 6 1

• -1 4
  % 7 8

• 2 3
  a -1 -1
  str -1 -1
  871 -1 -1
  Sample Output 2:
  (((a)(2.35)*)(-((str)(871)%))+)