<p>You are given a string <code>s</code> consisting only of characters <code>&#39;a&#39;</code> and <code>&#39;b&#39;</code>​​​​.</p>

<p>You can delete any number of characters in <code>s</code> to make <code>s</code> <strong>balanced</strong>. <code>s</code> is <strong>balanced</strong> if there is no pair of indices <code>(i,j)</code> such that <code>i &lt; j</code> and <code>s[i] = &#39;b&#39;</code> and <code>s[j]= &#39;a&#39;</code>.</p>

<p>Return <em>the <strong>minimum</strong> number of deletions needed to make </em><code>s</code><em> <strong>balanced</strong></em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;aababbab&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> You can either:
Delete the characters at 0-indexed positions 2 and 6 (&quot;aa<u>b</u>abb<u>a</u>b&quot; -&gt; &quot;aaabbb&quot;), or
Delete the characters at 0-indexed positions 3 and 6 (&quot;aab<u>a</u>bb<u>a</u>b&quot; -&gt; &quot;aabbbb&quot;).
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;bbaaaaabb&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> The only solution is to delete the first two characters.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s[i]</code> is&nbsp;<code>&#39;a&#39;</code> or <code>&#39;b&#39;</code>​​.</li>
</ul>

class Solution {
public:

    int popA(string s, stack<char> stk)
    {
        int count = 0;
        int n = s.size();
        for(int i=0; i<n; i++)
        {
            if( stk.empty() )
            {
                stk.push(s[i]);
            }
            else if( !stk.empty() && s[i] == 'a' && stk.top() == 'b' )
            {
                while( !stk.empty() && s[i] == 'a' && stk.top() == 'b' )
                {
                    stk.pop();
                    i++;
                    count++;
                }
                stk.push(s[i]);
            }
            else
            {
                stk.push(s[i]);
            }
        }

        return count;
    }

    // int popA(string s, stack<char> stk)
    // {
    //     int count = 0;
    //     int n = s.size();
    //     for(int i=0; i<n; i++)
    //     {
    //         if( stk.empty() )
    //         {
    //             stk.push(s[i]);
    //         }
    //         else if( !stk.empty() && s[i] == 'a' && stk.top() == 'b' )
    //         {
    //             while( i < n && s[i] == 'a' )
    //             {
    //                 i++;
    //                 count++;
    //             }
    //             stk.push(s[i]);
    //         }
    //         else
    //         {
    //             stk.push(s[i]);
    //         }
    //     }

    //     return count;
    // }
    int minimumDeletions(string s) {
        stack<char> stk;

        int a = popA(s, stk);
        // int b = popB(s, stk);

        // cout<<a<<" "<<b;
        return a;
    }
};
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