<p>Given a string <code>paragraph</code> and a string array of the banned words <code>banned</code>, return <em>the most frequent word that is not banned</em>. It is <strong>guaranteed</strong> there is <strong>at least one word</strong> that is not banned, and that the answer is <strong>unique</strong>.</p>

<p>The words in <code>paragraph</code> are <strong>case-insensitive</strong> and the answer should be returned in <strong>lowercase</strong>.</p>

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

<pre>
<strong>Input:</strong> paragraph = &quot;Bob hit a ball, the hit BALL flew far after it was hit.&quot;, banned = [&quot;hit&quot;]
<strong>Output:</strong> &quot;ball&quot;
<strong>Explanation:</strong> 
&quot;hit&quot; occurs 3 times, but it is a banned word.
&quot;ball&quot; occurs twice (and no other word does), so it is the most frequent non-banned word in the paragraph. 
Note that words in the paragraph are not case sensitive,
that punctuation is ignored (even if adjacent to words, such as &quot;ball,&quot;), 
and that &quot;hit&quot; isn&#39;t the answer even though it occurs more because it is banned.
</pre>

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

<pre>
<strong>Input:</strong> paragraph = &quot;a.&quot;, banned = []
<strong>Output:</strong> &quot;a&quot;
</pre>

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

<ul>
	<li><code>1 &lt;= paragraph.length &lt;= 1000</code></li>
	<li>paragraph consists of English letters, space <code>&#39; &#39;</code>, or one of the symbols: <code>&quot;!?&#39;,;.&quot;</code>.</li>
	<li><code>0 &lt;= banned.length &lt;= 100</code></li>
	<li><code>1 &lt;= banned[i].length &lt;= 10</code></li>
	<li><code>banned[i]</code> consists of only lowercase English letters.</li>
</ul>


class Solution {
public:
    string mostCommonWord(string paragraph, vector<string>& banned) {
        set<string>bannedst(banned.begin(),banned.end());
       transform(paragraph.begin(),paragraph.end(),paragraph.begin(),::tolower);
         int n=paragraph.size();
        stack<string>wordStack;
        string word="";
       for (int i = 0; i < n; i++) {
        if (isalpha(paragraph[i])) {
            // Accumulate alphabetic characters into a word
            word += paragraph[i];
        } else if (!word.empty()) {
            // Push the word into the stack if it's not empty
            wordStack.push(word);
            word = "";
        }
    }
    
    // If the last word wasn't added (paragraph doesn't end with punctuation)
    if (!word.empty()) {
        wordStack.push(word);
    }
    
   map<string,int>mpp;
    
    // Process each word from the stack and count the frequencies
    while (!wordStack.empty()) {
        string topWord = wordStack.top();
        wordStack.pop();
        
        // Count the word if it's not banned
        if (bannedst.find(topWord) == bannedst.end()) {
            mpp[topWord]++;
        }
    }
        int maxi=0;
        string ans="";
        for(auto i:mpp){
            if(i.second>maxi){
                if(bannedst.find(i.first)==bannedst.end()){
                    ans=i.first;
                     maxi=i.second;
                }
            }
            
        }
        return ans;
    }
};
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