1963. Minimum Number of Swaps to Make the String Balanced

https://leetcode.com/problems/minimum-number-of-swaps-to-make-the-string-balanced

Description

You are given a 0-indexed string s of even length n. The string consists of exactly n / 2 opening brackets '[' and n / 2 closing brackets ']'.

A string is called balanced if and only if:

• It is the empty string, or

• It can be written as AB, where both A and B are balanced strings, or

• It can be written as [C], where C is a balanced string.

You may swap the brackets at any two indices any number of times.

Return the minimum number of swaps to make s balanced.

Example 1:

**Input:** s = "][]["
**Output:** 1
**Explanation:** You can make the string balanced by swapping index 0 with index 3.
The resulting string is "[[]]".

Example 2:

**Input:** s = "]]][[["
**Output:** 2
**Explanation:** You can do the following to make the string balanced:
- Swap index 0 with index 4. s = "[]][][".
- Swap index 1 with index 5. s = "[[][]]".
The resulting string is "[[][]]".

Example 3:

**Input:** s = "[]"
**Output:** 0
**Explanation:** The string is already balanced.

Constraints:

• n == s.length

• 2 <= n <= 106

• n is even.

• s[i] is either '[' or ']'.

• The number of opening brackets '[' equals n / 2, and the number of closing brackets ']' equals n / 2.

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