LeetCode 最长回文子串算法

Manacher 算法 容易理解，实现起来也没什么大坑，复杂度还是 O(n)的， 花半个小时实现下很有意思

class Solution {
    public String longestPalindrome(String s) {        
        StringBuilder sb = new StringBuilder(2 + 2 * s.length());
        sb.append("^");
        for (int i = 0; i < s.length(); i++) {
            sb.append("#").append(s.charAt(i));
        }
        sb.append("#$");
        
        String s2 = sb.toString();
        
        int maxStart = 1, max = 0, rC = 1, rR = 1;
        int[] p = new int[s2.length()];
        
        for (int i = 1; i < s2.length() - 1; i++ ) {
            
            p[i] = i < rR ? Math.min(p[2 * rC - i], rR - i) : 0;
            
            while (s2.charAt(i+p[i]+1) == s2.charAt(i - p[i] - 1)) {
                p[i] = p[i]+1;
            }
            
            if (i + p[i] > rR) {
                rC = i;
                rR = i + p[i];
            }
            
            if (p[i] > max) {
                maxStart = i - p[i];
                max = p[i];
            }
        }
        

        return s2.substring(maxStart,maxStart + 2*max+1).replace("#", "");
    }
}