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Minimum Number of Swaps to Make the String Balanced

You are given a 0-indexed string s of even length n.

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:

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

Return the minimum number of swaps to make s balanced.

Minimum Number of Swaps to Make the String Balanced diagram

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 <= 10^6
  • 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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