leetcode5. Longest Palindromic S

求一个最长回文子串，使用中心探测法，向两边探测即可（当然马拉车算法也可以做）

class Solution {
    int max, left, right;
    public String longestPalindrome(String s) {
        if (s.length() == 0 || s.length() == 1) return s;
        for (int i = 0; i < s.length() - 1; i++) {
            // 奇偶情况
            judge(s, i, i);
            judge(s, i, i + 1);
        }
        return s.substring(left, right);
    }
    
    public void judge(String s, int lo, int hi) {
        int n = s.length();
        while (lo >= 0 && hi < n && s.charAt(lo) == s.charAt(hi)) {
            lo--;
            hi++;
        }
        if (hi - lo - 1 > max) {
            max = hi - lo - 1;
            left = lo + 1;
            right = hi;
        }
    }
}