[LeetCode] 131. Palindrome Partitioning

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.

A palindrome string is a string that reads the same backward as forward.

Example 1:

Input: s = "aab"
Output: [["a","a","b"],["aa","b"]]

Example 2:

Input: s = "a"
Output: [["a"]]

Constraints:

• 1 <= s.length <= 16
• s contains only lowercase English letters.

分割回文串。

题意是给一个字符串，请做适当分割，使得分割的子串都是回文串。

思路依然是回溯backtracking。

时间O(2^n)

空间O(n)

Java实现

class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> res = new ArrayList<>();
        if (s == null || s.length() == 0) {
            return res;
        }
        helper(res, new ArrayList<>(), s);
        return res;
    }

    private void helper(List<List<String>> res, List<String> list, String s) {
        if (s.length() == 0) {
            res.add(new ArrayList<>(list));
            return;
        }
        for (int i = 0; i < s.length(); i++) {
            if (isPalindrome(s.substring(0, i + 1))) {
                list.add(s.substring(0, i + 1));
                helper(res, list, s.substring(i + 1));
                list.remove(list.size() - 1);
            }
        }
    }

    private boolean isPalindrome(String s) {
        for (int i = 0; i < s.length() / 2; i++) {
            if (s.charAt(i) != s.charAt(s.length() - i - 1)) {
                return false;
            }
        }
        return true;
    }
}

LeetCode 题目总结