<p>Given a string <code>formula</code> representing a chemical formula, return <em>the count of each atom</em>.</p>

<p>The atomic element always starts with an uppercase character, then zero or more lowercase letters, representing the name.</p>

<p>One or more digits representing that element&#39;s count may follow if the count is greater than <code>1</code>. If the count is <code>1</code>, no digits will follow.</p>

<ul>
	<li>For example, <code>&quot;H2O&quot;</code> and <code>&quot;H2O2&quot;</code> are possible, but <code>&quot;H1O2&quot;</code> is impossible.</li>
</ul>

<p>Two formulas are concatenated together to produce another formula.</p>

<ul>
	<li>For example, <code>&quot;H2O2He3Mg4&quot;</code> is also a formula.</li>
</ul>

<p>A formula placed in parentheses, and a count (optionally added) is also a formula.</p>

<ul>
	<li>For example, <code>&quot;(H2O2)&quot;</code> and <code>&quot;(H2O2)3&quot;</code> are formulas.</li>
</ul>

<p>Return the count of all elements as a string in the following form: the first name (in sorted order), followed by its count (if that count is more than <code>1</code>), followed by the second name (in sorted order), followed by its count (if that count is more than <code>1</code>), and so on.</p>

<p>The test cases are generated so that all the values in the output fit in a <strong>32-bit</strong> integer.</p>

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

<pre>
<strong>Input:</strong> formula = &quot;H2O&quot;
<strong>Output:</strong> &quot;H2O&quot;
<strong>Explanation:</strong> The count of elements are {&#39;H&#39;: 2, &#39;O&#39;: 1}.
</pre>

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

<pre>
<strong>Input:</strong> formula = &quot;Mg(OH)2&quot;
<strong>Output:</strong> &quot;H2MgO2&quot;
<strong>Explanation:</strong> The count of elements are {&#39;H&#39;: 2, &#39;Mg&#39;: 1, &#39;O&#39;: 2}.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> formula = &quot;K4(ON(SO3)2)2&quot;
<strong>Output:</strong> &quot;K4N2O14S4&quot;
<strong>Explanation:</strong> The count of elements are {&#39;K&#39;: 4, &#39;N&#39;: 2, &#39;O&#39;: 14, &#39;S&#39;: 4}.
</pre>

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

<ul>
	<li><code>1 &lt;= formula.length &lt;= 1000</code></li>
	<li><code>formula</code> consists of English letters, digits, <code>&#39;(&#39;</code>, and <code>&#39;)&#39;</code>.</li>
	<li><code>formula</code> is always valid.</li>
</ul>

#include <string>
#include <unordered_map>
#include <stack>
#include <cctype>
#include <map>

class Solution {
public:
    string countOfAtoms(string formula) {
        int n = formula.size();
        stack<unordered_map<string, int>> st;
        unordered_map<string, int> current;
        int i = 0;
        
        while (i < n) {
            if (formula[i] == '(') {
                
                st.push(current);
                current.clear();
                i++;
            } else if (formula[i] == ')') {
                i++;
                int start = i;
                while (i < n && isdigit(formula[i])) i++; 
                int multiplier = (start < i) ? stoi(formula.substr(start, i - start)) : 1;
                
                // Multiply the current map and merge it with the top of the stack
                unordered_map<string, int> top = st.top(); st.pop();
                for (auto &[atom, count] : current) {
                    top[atom] += count * multiplier;
                }
                current = top;
            } else {
                
                int start = i++;
                while (i < n && islower(formula[i])) i++;
                string atom = formula.substr(start, i - start);
                
                
                start = i;
                while (i < n && isdigit(formula[i])) i++;
                int count = (start < i) ? stoi(formula.substr(start, i - start)) : 1;
                
                
                current[atom] += count;
            }
        }
        
        
        map<string, int> sortedAtoms(current.begin(), current.end());
        string result;
        for (auto &[atom, count] : sortedAtoms) {
            result += atom;
            if (count > 1) result += to_string(count);
        }
        
        return result;
    }
};

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