Manacher

 

public class T05_02_Manacher {

    public String longestPalindrome(String s) {
        /***
         * Manacher 返回 字符串长度
         *
         */
        //1.将字符串处理成Manacher字符串

        //2.新建数组，记录相应位置的长度值，，，并且记录最右侧边缘，和对应的i

        //3.遍历字符串。判断此点是否在右侧边缘以内，若在边缘引内，

        char[] charArray = manacher(s);
        int[] pArray = new int[charArray.length];
        int pR = -1;
        int index = -1;
        int max = 0;
        for (int i = 0; i < charArray.length; i++) {
            pArray[i] = i < pR ? Math.min(pArray[2 * index - i], pR - i) : 1;
            while (i + pArray[i] < charArray.length && i - pArray[i] >= 0) {
                if (charArray[i + pArray[i]] == charArray[i - pArray[i]]) {
                    pArray[i]++;
                } else {
                    break;
                }
            }

            if (pArray[i] + i > pR) {
                pR = pArray[i] + i;
                index = i;
            }
            max = Math.max(max, pArray[i]);
        }
        int maxIndex = 0;
        for (int i = 0; i < pArray.length; i++) {
            if (pArray[i] == max) {
                maxIndex = i;
                break;
            }
        }
        return s.substring((maxIndex - max + 2) / 2, (maxIndex - max + 2) / 2 + max - 1);

    }

    private char[] manacher(String s) {
        String str = "#";
        for (int i = 0; i < s.length(); i++) {
            str += s.charAt(i) + "#";
        }
        return str.toCharArray();

    }
}