<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>

class Solution {
public:
    vector<vector<string>> partition(string s) {
        vector<string> pf;
        vector<vector<string>> ans;
        ans = solve(s, pf);
        return ans;
    }

    unordered_map<string, bool> pals;
    bool isPalindrome(string s) {
        if (s.length() == 1) {
            return true;
        }
        if (pals.contains(s)) {
            return pals[s];
        }
        int lo = 0, hi = s.length()-1;
        bool flag = true;
        while (lo < hi) {
            if (s[lo++] != s[hi--]) {
                flag = false; break;
            }
        }
        pals[s] = flag;
        return flag;
    }

    unordered_map<string, vector<vector<string>>> parts;
    vector<vector<string>> solve(string s, vector<string> &pf) {
        if (parts.contains(s)) return parts[s];
        vector<vector<string>> partitions;
        for (int len = 1; len < s.length(); len++) {
            string l = s.substr(0, len);
            string r = s.substr(len, s.length());
            if (isPalindrome(l)) {
                pf.push_back(l);
                auto sml = solve(r, pf);
                pf.pop_back();
                for (int i = 0; i < sml.size(); i++) {
                    sml[i].insert(sml[i].begin(), l);
                    partitions.push_back(sml[i]);
                }
            }
        }
        if (isPalindrome(s)) {
            partitions.push_back({s});
        }
        parts[s] = partitions;
        return partitions;
    }
};

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