LintCode 分割回文串题目分析代码

public class Solution {
    /**
     * @param s: A string
     * @return: A list of lists of string
     */
    
    List<List<String>> results;
    boolean[][] isPalindrome;
    
    /**
     * @param s: A string
     * @return: A list of lists of string
     */
    public List<List<String>> partition(String s) {
        results = new ArrayList<>();
        if (s == null || s.length() == 0) {
            return results;
        }
        
        getIsPalindrome(s);
        
        helper(s, 0, new ArrayList<Integer>());
        
        return results;
    }
    
    private void getIsPalindrome(String s) {
        int n = s.length();
        isPalindrome = new boolean[n][n];
        
        for (int i = 0; i < n; i++) {
            isPalindrome[i][i] = true;
        }
        for (int i = 0; i < n - 1; i++) {
            isPalindrome[i][i + 1] = (s.charAt(i) == s.charAt(i + 1));
        }
        
        for (int i = n - 3; i >= 0; i--) {
            for (int j = i + 2; j < n; j++) {
                isPalindrome[i][j] = isPalindrome[i + 1][j - 1] && s.charAt(i) == s.charAt(j);
            }
        }
    }
    
    private void helper(String s,
                        int startIndex,
                        List<Integer> partition) {
        if (startIndex == s.length()) {
            addResult(s, partition);
            return;
        }
        
        for (int i = startIndex; i < s.length(); i++) {
            if (!isPalindrome[startIndex][i]) {
                continue;
            }
            partition.add(i);
            helper(s, i + 1, partition);
            partition.remove(partition.size() - 1);
        }
    }
    
    private void addResult(String s, List<Integer> partition) {
        List<String> result = new ArrayList<>();
        int startIndex = 0;
        for (int i = 0; i < partition.size(); i++) {
            result.add(s.substring(startIndex, partition.get(i) + 1));
            startIndex = partition.get(i) + 1;
        }
        results.add(result);
    }
}