Given a syntax tree (binary), you are supposed to output the corresponding infix expression, with parentheses reflecting the precedences of the operators.
Each input file contains one test case. For each case, the first line gives a positive integer $N (\leqslant 20)$ 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.
For each case, print in a line the infix expression, with parentheses reflecting the precedences of the operators. Note that there must be no extra parentheses for the final expression, as is shown by the samples. There must be no space between any symbols.
8
* 8 7
a -1 -1
* 4 1
+ 2 5
b -1 -1
d -1 -1
- -1 6
c -1 -1
(a+b)*(c*(-d))
8
2.35 -1 -1
* 6 1
- -1 4
% 7 8
+ 2 3
a -1 -1
str -1 -1
871 -1 -1
(a*2.35)+(-(str%871))
本题 25 分，
class BTNode:
def __init__(self, val):
self.val = val
self.left = None
self.right = None
class BT():
def insert(self, root, node, index):
val, left, right = node[index][0], node[index][1], node[index][2]
if left != -1:
root.left = BTNode(node[left][0])
root.left = self.insert(root.left, node, left)
if right != -1:
root.right = BTNode(node[right][0])
root.right = self.insert(root.right, node, right)
return root
def in_order(self, root, lst, depth):
if root == None: return
if depth and (root.left or root.right): lst.append('(')
self.in_order(root.left, lst, depth+1)
lst.append(root.val)
self.in_order(root.right, lst, depth+1)
if depth and (root.left or root.right): lst.append(')')
def find_root(nodes):
pool = set([i+1 for i in range(len(nodes))])
for node in nodes:
pool -= set(node[1:])
return pool.pop()
nodes = []
result = []
count = int(input())
for _ in range(count):
val, left, right = input().split()
nodes.append((val, int(left), int(right)))
head = find_root(nodes)
nodes.insert(0, head)
bt = BT()
tree = BTNode(nodes[head][0])
bt.insert(tree, nodes, head)
bt.in_order(tree, result, 0)
print(''.join(result))
https://www.amoshuang.com/archives/589
https://blog.csdn.net/galesaur_wcy/article/details/82354161
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https://blog.csdn.net/weixin_43307431/article/details/104364778