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package class28;
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public class Code01_Manacher {
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public static int manacher(String s) {
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if (s == null || s.length() == 0) {
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return 0;
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}
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// "12132" -> "#1#2#1#3#2#"
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char[] str = manacherString(s);
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// 回文半径的大小
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int[] pArr = new int[str.length];
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int C = -1;
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// 讲述中：R代表最右的扩成功的位置
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// coding：最右的扩成功位置的，再下一个位置
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int R = -1;
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int max = Integer.MIN_VALUE;
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for (int i = 0; i < str.length; i++) { // 0 1 2
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// R第一个违规的位置，i>= R
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// i位置扩出来的答案，i位置扩的区域，至少是多大。
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pArr[i] = R > i ? Math.min(pArr[2 * C - i], R - i) : 1;
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while (i + pArr[i] < str.length && i - pArr[i] > -1) {
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if (str[i + pArr[i]] == str[i - pArr[i]])
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pArr[i]++;
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else {
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break;
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}
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}
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if (i + pArr[i] > R) {
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R = i + pArr[i];
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C = i;
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}
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max = Math.max(max, pArr[i]);
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}
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return max - 1;
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}
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public static char[] manacherString(String str) {
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char[] charArr = str.toCharArray();
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char[] res = new char[str.length() * 2 + 1];
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int index = 0;
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for (int i = 0; i != res.length; i++) {
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res[i] = (i & 1) == 0 ? '#' : charArr[index++];
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}
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return res;
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}
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// for test
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public static int right(String s) {
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if (s == null || s.length() == 0) {
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return 0;
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}
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char[] str = manacherString(s);
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int max = 0;
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for (int i = 0; i < str.length; i++) {
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int L = i - 1;
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int R = i + 1;
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while (L >= 0 && R < str.length && str[L] == str[R]) {
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L--;
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R++;
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}
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max = Math.max(max, R - L - 1);
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}
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return max / 2;
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}
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// for test
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public static String getRandomString(int possibilities, int size) {
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char[] ans = new char[(int) (Math.random() * size) + 1];
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for (int i = 0; i < ans.length; i++) {
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ans[i] = (char) ((int) (Math.random() * possibilities) + 'a');
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}
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return String.valueOf(ans);
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}
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public static void main(String[] args) {
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int possibilities = 5;
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int strSize = 20;
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int testTimes = 5000000;
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System.out.println("test begin");
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for (int i = 0; i < testTimes; i++) {
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String str = getRandomString(possibilities, strSize);
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if (manacher(str) != right(str)) {
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System.out.println("Oops!");
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}
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}
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System.out.println("test finish");
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}
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}
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