Longest Palindromic Substring

题目

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

方法

以时间换空间的方法。 子串[i, j] 是回文串的要求是： 字符(i) == 字符(j) 且子串[i + 1, j - 1]也是回文串。每次将结果保存。

    public String longestPalindrome(String s) {
        if (s == null) {
            return null;
        }
        if (s.length() <= 1) {
            return s;
        }
        int len = s.length();
        boolean[][] status = new boolean[len][len];
        for (int interval = 0; interval < len; interval++) {
            for (int i = 0; i < len - interval; i++) {
                int j = i + interval;
                if (i == j) {
                    status[i][j] = true;
                } else if (s.charAt(i) == s.charAt(j)) {
                    if (i + 1 < j - 1) {
                        if (status[i + 1][j - 1] == true) {
                            status[i][j] = true;
                        }
                    } else {
                        status[i][j] = true;
                    }
                }
            }
        }
        
        
        int left = 0;
        int right = 0;
        for (int interval = 0; interval < len; interval++) {
            for (int i = 0; i < len - interval; i++) {
                int j = i + interval;
                if (status[i][j] == true) {
                    left = i;
                    right = j;
                    break;
                }
            }
        }
        return s.substring(left, right + 1);
        
    }