leetcode 1021. Remove Outermost Parentheses （python）
描述
A valid parentheses string is either empty (""), "(" + A + ")", or A + B, where A and B are valid parentheses strings, and + represents string concatenation. For example, "", "()", "(())()", and "(()(()))" are all valid parentheses strings.
A valid parentheses string S is primitive if it is nonempty, and there does not exist a way to split it into S = A+B, with A and B nonempty valid parentheses strings.
Given a valid parentheses string S, consider its primitive decomposition: S = P_1 + P_2 + ... + P_k, where P_i are primitive valid parentheses strings.
Return S after removing the outermost parentheses of every primitive string in the primitive decomposition of S.
Example 1:
Input: "(()())(())"
Output: "()()()"
Explanation:
The input string is "(()())(())", with primitive decomposition "(()())" + "(())".
After removing outer parentheses of each part, this is "()()" + "()" = "()()()".
Example 2:
Input: "(()())(())(()(()))"
Output: "()()()()(())"
Explanation:
The input string is "(()())(())(()(()))", with primitive decomposition "(()())" + "(())" + "(()(()))".
After removing outer parentheses of each part, this is "()()" + "()" + "()(())" = "()()()()(())".
Example 3:
Input: "()()"
Output: ""
Explanation:
The input string is "()()", with primitive decomposition "()" + "()".
After removing outer parentheses of each part, this is "" + "" = "".
Note:
S.length <= 10000
S[i] is "(" or ")"
S is a valid parentheses string
解析
根据题意，合法的括号子字符串就是左右括号数相等即可，然后去掉最外层的左右括号，将剩下的合法的括号子字符串都拼接起来返回即可，具体看例子一就可清楚。其实和以前的括号题一样，只需要通过对左括号计数加一，对右括号计数减一，当计数器变为零的时候，表示找到一组合法的括号子字符串，然后只截取除最外层括号外的字符串追加到 res 中即可，继续遍历后面的字符串执行如上相同的操作，遍历结束得到的 res 即为结果。
解答
class Solution(object):
def removeOuterParentheses(self, S):
"""
:type S: str
:rtype: str
"""
count = 0
res = ''
idx = 0
for i, c in enumerate(S):
if c == '(':
count += 1
elif c == ')':
count -= 1
if count == 0:
res += S[idx + 1: i]
idx = i + 1
return res
运行结果
Runtime: 24 ms, faster than 91.36% of Python online submissions for Remove Outermost Parentheses.
Memory Usage: 13.8 MB, less than 66.24% of Python online submissions for Remove Outermost Parentheses.
原题链接：leetcode.com/problems/re…
您的支持是我最大的动力
