Given a string s, partition s such that every substring of the partition is a palindrome.

Return all possible palindrome partitioning of s.

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Input: "aab"
Output:
[
  ["aa","b"],
  ["a","a","b"]
]
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class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> list = new ArrayList<>();
        dfs(list, new ArrayList<>(), s, 0);
        return list;
    }
    
    public void dfs(List<List<String>> list, List<String> arr, String s, int start) {
        if (start == s.length()) list.add(new ArrayList<>(arr));
        else {
            for (int i = start; i < s.length(); ++i) {
                if (isPalindrome(s, start, i)) {
                    arr.add(s.substring(start, i + 1));
                    dfs(list, arr, s, i + 1);
                    arr.remove(arr.size() - 1);
                }
            }
        }
    }
    
    public boolean isPalindrome(String s, int start, int end) {
        while (start < end) {
            if (s.charAt(start++) != s.charAt(end--)) return false;
        }
        return true;
    }
}