536. Construct Binary Tree from String
难度: 中等
刷题内容
原题连接
- https://leetcode.com/problems/construct-binary-tree-from-string
内容描述
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:
There will only be '(', ')', '-' and '0' ~ '9' in the input string.
An empty tree is represented by "" instead of "()".
解题方案
思路 1
递归，每次先找到左子树，然后判断有无右子树，继续下去
class Solution(object):
def str2tree(self, s):
"""
:type s: str
:rtype: TreeNode
"""
if not s or len(s) == 0:
return None
if '(' not in s:
return TreeNode(int(s))
def paren_pair_idx(s):
paren_count = 0
for i in range(len(s)):
if s[i] == '(':
paren_count += 1
elif s[i] == ')':
paren_count -= 1
if paren_count == 0 and i > s.find('('):
return (s.find('('), i)
root = TreeNode(int(s[:s.find('(')]))
(paren_left, paren_right) = paren_pair_idx(s)
root.left = self.str2tree(s[paren_left+1: paren_right])
if paren_right < len(s) - 1:
root.right = self.str2tree(s[paren_right+2:-1])
else:
root.right = None
return root
