1653. Minimum Deletions to Make String Balanced

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