<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) {
        std::vector<std::pair<std::string, int>> words;
        std::string word;

        for (int i = 0; i < paragraph.size(); ++i) {
            switch (paragraph[i]) {
            case ' ':
            case '.':
            case ',':
            case '!':
            case '?':
            case ';':
            case '\'':
                if (!word.empty()) {

                    bool isBanned = false;
                    for (const auto& b : banned) {
                        if (b == word) {
                            isBanned = true;
                            break;
                        }
                    }
                    if (!isBanned) {

                        bool found = false;
                        for (auto& x : words) {
                            if (x.first == word) {
                                x.second += 1;
                                found = true;
                                break;
                            }
                        }
                        if (!found) {
                            words.push_back({word, 1});
                        }
                    }
                    word = "";
                }
                break;
            default:
                word += std::tolower(paragraph[i]);
                break;
            }
        }

        if (!word.empty()) {
            bool isBanned = false;
            for (const auto& b : banned) {
                if (b == word) {
                    isBanned = true;
                    break;
                }
            }
            if (!isBanned) {
                bool found = false;
                for (auto& x : words) {
                    if (x.first == word) {
                        x.second += 1;
                        found = true;
                        break;
                    }
                }
                if (!found) {
                    words.push_back({word, 1});
                }
            }
        }
        auto res = words[0];
        if (!words.empty()) {
            
            for (const auto& x : words) {
                if (x.second > res.second) {
                    res = x;
                }
            }
            
        }
        return res.first;
    }
};
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