Given a string s consisting only of the characters 'a' and 'b'.

A string is considered balanced if there is no pair of indices (i, j) such that $i < j$, s[i] is equal to 'b', and s[j] is equal to 'a'.

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

Constraints:

• $1 \leq$ s.length $\leq 10^5$

• s[i] is either 'a' or 'b'

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We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.