<p>Given two strings <code>s</code> and <code>p</code>, return <em>an array of all the start indices of </em><code>p</code><em>&#39;s anagrams in </em><code>s</code>. You may return the answer in <strong>any order</strong>.</p>

<p>An <strong>Anagram</strong> is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.</p>

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

<pre>
<strong>Input:</strong> s = &quot;cbaebabacd&quot;, p = &quot;abc&quot;
<strong>Output:</strong> [0,6]
<strong>Explanation:</strong>
The substring with start index = 0 is &quot;cba&quot;, which is an anagram of &quot;abc&quot;.
The substring with start index = 6 is &quot;bac&quot;, which is an anagram of &quot;abc&quot;.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;abab&quot;, p = &quot;ab&quot;
<strong>Output:</strong> [0,1,2]
<strong>Explanation:</strong>
The substring with start index = 0 is &quot;ab&quot;, which is an anagram of &quot;ab&quot;.
The substring with start index = 1 is &quot;ba&quot;, which is an anagram of &quot;ab&quot;.
The substring with start index = 2 is &quot;ab&quot;, which is an anagram of &quot;ab&quot;.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length, p.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>s</code> and <code>p</code> consist of lowercase English letters.</li>
</ul>

#include <vector>
#include <unordered_set>

class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        std::vector<int> start_indices;
        int n = s.size();
        int l = p.size();

        std::vector<int> anagram_count(26, 0);
        std::unordered_set<char> anagram_set(p.begin(), p.end());

        for (int i = 0; i < l; i++)
        {
            anagram_count[p[i] - 'a']++;
        }

        for (int i = 0; i < (n - l + 1); i++)
        {
            int j = l + i - 1;
            if (isAnagram(s, i, j, anagram_count, anagram_set))
            {
                start_indices.push_back(i);
            }
        }

        return start_indices;
    }

private:
    bool isAnagram(const std::string& s, int i, int j, std::vector<int> anagram_count, std::unordered_set<char>& anagram_set)
    {
        for (int k = i; k <= j; k++)
        {
            if (anagram_set.find(s[k]) == anagram_set.end()) return false;
            anagram_count[s[k] - 'a']--;
        }

        for (const auto& count : anagram_count)
        {
            if (count != 0) return false;
        }

        return true;
    }
};
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