1130 Infix Expression - (25分)

题目

Given a syntax tree (binary), you are supposed to output the corresponding infix 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 $N(\le 20)$ 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 righ