Leetcode 1249. Minimum Remove to Make Valid Parentheses

Gary Chiang
1 min readAug 23, 2021

[medium]

Given a string s of '(' , ')' and lowercase English characters.

Your task is to remove the minimum number of parentheses ( '(' or ')', in any positions ) so that the resulting parentheses string is valid and return any valid string.

Formally, a parentheses string is valid if and only if:

  • It is the empty string, contains only lowercase characters, or
  • It can be written as AB (A concatenated with B), where A and B are valid strings, or
  • It can be written as (A), where A is a valid string.

Example 1:

Input: s = "lee(t(c)o)de)"
Output: "lee(t(c)o)de"
Explanation: "lee(t(co)de)" , "lee(t(c)ode)" would also be accepted.

Example 2:

Input: s = "a)b(c)d"
Output: "ab(c)d"

Example 3:

Input: s = "))(("
Output: ""
Explanation: An empty string is also valid.

Example 4:

Input: s = "(a(b(c)d)"
Output: "a(b(c)d)"

Constraints:

  • 1 <= s.length <= 10^5
  • s[i] is one of '(' , ')' and lowercase English letters.

[Java]

  1. Think: use stack to store all the ‘(‘, if we find ’)’, and stack is not empty, pop from the stack.
  2. used any non-alphbet character to be a place holder, and remove them at the end
  3. use stringbuilder function : setCharAt(position, ‘?’) to modify the string
  4. use toString() function to change from StringBuilder to String

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Gary Chiang

CS new grad, 6 years experience related to supply chain management. Located in Bay area