131 Palindrome Partitioning

Given a strings, partition_s _such that every substring of the partition is a palindrome.

Return all possible palindrome partitioning ofs.

Example:

Input:
 "aab"

Output:

[
  ["aa","b"],
  ["a","a","b"]
]

Backtracking

class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> ans = new ArrayList<>();
        if (s == null || s.length() == 0) {
            return ans;
        }
        List<String> part = new ArrayList<>();
        helper(ans, part, 0, s);
        return ans;
    }
    public void helper(List<List<String>> ans, List<String> part, int startIdx, String s) {
        if (startIdx == s.length()) {
            ans.add(new ArrayList<>(part));
        }
        for(int i = startIdx; i < s.length(); i++) {
            String str = s.substring(startIdx, i + 1);
            if(!isPalindrome(str)) {
                continue;
            }
            part.add(str);
            helper(ans, part, i + 1, s);
            part.remove(part.size() - 1);
        }
    }
    public boolean isPalindrome(String s) {
        int start = 0;
        int end = s.length() - 1;
        // abba
        //aba
        while (start < end){
            if (s.charAt(start) == s.charAt(end)) {
                start++;
                end--;
            }else {
                return false;
            }
        }
        return true;
    }
}