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50 lines
1.0 KiB
50 lines
1.0 KiB
2 years ago
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package class38;
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public class Problem_0647_PalindromicSubstrings {
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public static int countSubstrings(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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int[] dp = getManacherDP(s);
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int ans = 0;
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for (int i = 0; i < dp.length; i++) {
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ans += dp[i] >> 1;
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}
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return ans;
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}
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public static int[] getManacherDP(String s) {
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char[] str = manacherString(s);
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int[] pArr = new int[str.length];
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int C = -1;
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int R = -1;
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for (int i = 0; i < str.length; i++) {
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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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}
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return pArr;
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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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}
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