<p>Given a string array <code>words</code>, return <em>an array of all characters that show up in all strings within the </em><code>words</code><em> (including duplicates)</em>. You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> words = ["bella","label","roller"]
<strong>Output:</strong> ["e","l","l"]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> words = ["cool","lock","cook"]
<strong>Output:</strong> ["c","o"]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= words.length &lt;= 100</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 100</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
</ul>

class Solution {
public:
    vector<string> commonChars(vector<string>& words) {
        unordered_map<char, int> key_map;
        for (char c : words[0]) {
            key_map[c]++;
        }
        for (int i = 1; i < words.size(); i++) {
            unordered_map<char, int> duplicate_map;
            for (char c : words[i]) {
                duplicate_map[c]++;
            }
            for (auto& [key, val] : key_map) {
                if (duplicate_map.find(key) != duplicate_map.end()) {
                    key_map[key] = min(key_map[key], duplicate_map[key]);
                } else {
                    key_map[key] = 0;
                }
            }
        }
        vector<string> result;
        for (auto& [key, val] : key_map) {
            for (int i = 0; i < val; i++) {
                result.push_back(string(1, key));
            }
        }
        return result;
    }
};
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