class Solution {
public:
vector<vector<string>> partition(string s) {
int n = s.size();
vector<vector<string>> res;
vector<string> out;
vector<vector<bool>> dp(n, vector<bool>(n));
for (int i = 0; i < n; ++i) {
for (int j = 0; j <= i; ++j) {
if (s[i] == s[j] && (i - j <= 2 || dp[j + 1][i - 1])) {
dp[j][i] = true;
}
}
}
helper(s, 0, dp, out, res);
return res;
}
void helper(string s, int start, vector<vector<bool>>& dp, vector<string>& out, vector<vector<string>>& res) {
if (start == s.size()) { res.push_back(out); return; }
for (int i = start; i < s.size(); ++i) {
if (!dp[start][i]) continue;
out.push_back(s.substr(start, i - start + 1));
helper(s, i + 1, dp, out, res);
out.pop_back();
}
}
};