PAT-2019年秋季考试-甲级 7-3 后缀表达式(Postfix Expressions) (25 分)

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于 2019-09-09 14:41:54 发布

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该博客介绍了如何根据给定的语法树（二叉树）生成后缀表达式，要求输出的后缀表达式能反映出操作符的优先级，并提供了输入输出规格说明及样例。博主详细解释了针对不同节点状态（如左右孩子都为空、左孩子为空右孩子非空、左右孩子都非空）的处理策略。

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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, re

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