1653. Minimum Deletions to Make String Balanced

https://leetcode.com/problems/minimum-deletions-to-make-string-balanced

Description

You are given a string s consisting only of characters 'a' and 'b'​​​​.

You can delete any number of characters in s to make s balanced. s is balanced if there is no pair of indices (i,j) such that i < j and s[i] = 'b' and s[j]= 'a'.

Return the minimum number of deletions needed to make s balanced.

Example 1:

**Input:** s = "aababbab"
**Output:** 2
**Explanation:** You can either:
Delete the characters at 0-indexed positions 2 and 6 ("aababbab" -> "aaabbb"), or
Delete the characters at 0-indexed positions 3 and 6 ("aababbab" -> "aabbbb").

Example 2:

**Input:** s = "bbaaaaabb"
**Output:** 2
**Explanation:** The only solution is to delete the first two characters.

Constraints:

• 1 <= s.length <= 105

• s[i] is 'a' or 'b'​​.

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