<p>Given a string <code>s</code>, partition <code>s</code> such that every <span data-keyword="substring-nonempty">substring</span> of the partition is a <span data-keyword="palindrome-string"><strong>palindrome</strong></span>. Return <em>all possible palindrome partitioning of </em><code>s</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "aab"
<strong>Output:</strong> [["a","a","b"],["aa","b"]]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "a"
<strong>Output:</strong> [["a"]]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 16</code></li>
	<li><code>s</code> contains only lowercase English letters.</li>
</ul>

using palindromes = std::vector<std::vector<std::string>>;
using st = std::vector<std::string>;

class Solution {
private:
    palindromes ans;
    bool isPalindrome(std::string s)
    {
        bool res = true;
        int n = s.length();
        for (int i = 0; i < n / 2; i++)
          if (s[i] != s[n - i - 1])
          {
             res = false;
             break;
          }
        return res;
    }
    void backtrack(const std::string& s, int idx, st xs, palindromes& ans)
    {
        if(idx == s.size())
        {
            bool res = true;
            for(auto x : xs)
            {
                if(!isPalindrome(x))
                {
                    res = false;
                    break;
                }
            }
            if(res) ans.push_back(xs);
            return;
        }

        auto ys = xs;
        ys.push_back(s.substr(idx, 1));
        backtrack(s, idx + 1, ys, ans);
        if(!ys.empty())
        {
            ys.pop_back();
            if(ys.size() >= 1)
            {
                auto p = ys.back();
                ys[ys.size() - 1] = p + s.substr(idx, 1);
                backtrack(s, idx + 1, ys, ans);
            }
        }
    }
public:
    vector<vector<string>> partition(string s) 
    {
        palindromes ans;
        backtrack(s, 0, {}, ans);
        return ans; 
    }
};
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