概念：求字符串的最大回文串
1.先处理成偶数串
2.回文半径
3.回文半径最右边界，并记录最早中心位置
package basic_class_02;
public class Code_04_Manacher {
public static char[] manacherString(String str) {
char[] charArr = str.toCharArray();
char[] res = new char[str.length() * 2 + 1];
int index = 0;
for (int i = 0; i != res.length; i++) {
res[i] = (i & 1) == 0 ? '#' : charArr[index++];
}
return res;
}
public static int maxLcpsLength(String str) {
if (str == null || str.length() == 0) {
return 0;
}
char[] charArr = manacherString(str);
int[] pArr = new int[charArr.length];
int index = -1;
int pR = -1;
int max = Integer.MIN_VALUE;
for (int i = 0; i != charArr.length; i++) {
pArr[i] = pR > i ? Math.min(pArr[2 * index - i], pR - i) : 1;
while (i + pArr[i] < charArr.length && i - pArr[i] > -1) {
if (charArr[i + pArr[i]] == charArr[i - pArr[i]])
pArr[i]++;
else {
break;
}
}
if (i + pArr[i] > pR) {
pR = i + pArr[i];
index = i;
}
max = Math.max(max, pArr[i]);
}
return max - 1;
}
public static void main(String[] args) {
String str1 = "abc1234321ab";
System.out.println(maxLcpsLength(str1));
}
}
扩展题
给定一个字符串str1， 只能往str1的后面添加字符变成str2， 要求str2
整体都是回文串且最短。
举例：
str1 = ABC12321, 返回ABC12321CBA
