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@@ -0,0 +1,124 @@
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+<?php
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+
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+ /* Algorithm for finding (sub)palindromes in phrase
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+ Note: if there are spaces, they will be ignored
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+ and the string will be treated as if they weren't there.
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+ Also, all duplicates will not be included in result.
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+
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+ Manacher's Algorithm used here.
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+ */
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+
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+ mb_internal_encoding("UTF-8"); // UTF-8 support
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+
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+ class Palindrome {
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+
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+ public $subpalindromes;
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+ public $success;
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+ public $fail;
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+
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+ function __construct() {
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+ $this->subpalindromes = function ($phrase) {
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+ $phrase = mb_strtolower($phrase); // mb_* functions used to support UTF-8 encoding.
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+ $phrase = mb_ereg_replace(" ", "", $phrase); // remove all spaces
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+
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+
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+ $manacher_subpalindromes = self::manacher($phrase); // run Manacher's algorithm to find odd and even subpalindromes
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+ $odd_subpalindromes = $manacher_subpalindromes[0];
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+ $even_subpalindromes = $manacher_subpalindromes[1];
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+
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+ $palindromes = [];
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+ for ($i = 0; $i < mb_strlen($phrase); $i++) {
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+ if ($odd_subpalindromes[$i] > 1) { // ignore palindromes which consits of one character
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+ $palindromeLength = $odd_subpalindromes[$i]; // $odd_subpalindromes represents array of lengths of biggest palindromes, where index is the index of the character, which is the center of this palindrome
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+ while ($palindromeLength > 1) {
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+ $palindromes[] = mb_substr($phrase, $i - $palindromeLength + 1, $palindromeLength*2 - 1);
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+ $palindromeLength--;
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+ }
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+ }
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+
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+ // same as previous with specific changes
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+ if ($even_subpalindromes[$i] > 0) {
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+ $palindromeLength = $even_subpalindromes[$i];
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+ while ($palindromeLength > 0) {
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+ $palindromes[] = mb_substr($phrase, $i - $palindromeLength, $palindromeLength*2);
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+ $palindromeLength--;
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+ }
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+ }
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+ }
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+ return array_values(array_unique($palindromes));
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+ };
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+
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+ /* Used for formatting correct success message
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+ depending on the number of words found.
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+ */
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+ $this->success = function ($n) {
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+ $n_1 = $n % 100;
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+
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+ if ($n_1 > 19) {
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+ $n_1 = $n_1 % 10;
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+ }
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+
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+ $palindromeWordForm = "палиндром";
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+ $foundWordForm = "Найдено";
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+
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+ if ($n_1 >= 2 && $n_1 <= 4) {
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+ $palindromeWordForm = "палиндрома";
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+ } else if ($n_1 == 1) {
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+ $palindromeWordForm = "палиндром";
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+ $foundWordForm = "Найден";
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+ } else {
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+ $palindromeWordForm = "палиндромов";
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+ }
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+
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+ return $foundWordForm." ".strval($n)." ".$palindromeWordForm;
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+ };
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+
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+ $this->fail = "Не найдено ни одного палиндрома";
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+ }
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+
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+
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+
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+ /* Manacher's algorithm.
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+ Time complexity: O(n)
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+ Space complexity: O(1)
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+ */
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+ private static function manacher($str) {
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+ $n = mb_strlen($str);
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+ $odd = array_fill(0, $n, 0); // odd subpalindromes
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+ $even = array_fill(0, $n, 0); // even subpalindromes
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+
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+ /* Odd subpalindromes */
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+ $l = 0; // left edge of current rightest palindrome
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+ $r = -1; // right edge of current rightst palindrome
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+ for ($i = 0; $i < $n; $i++) {
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+ $k = $i > $r ? 1 : min($odd[$l + $r - $i], $r - $i + 1); // k - known via previous steps palindrome center offset (guaranteed biggest palindrome with center in current position [i-k, i+k]
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+ while ($i + $k < $n && $i - $k >= 0 && mb_substr($str, $i - $k, 1) == mb_substr($str, $i + $k, 1)) {
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+ $k++; // increment offset if we are still between 0 and string length and mirrored elements are equal
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+ }
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+ $odd[$i] = $k; // here we know max palindrome size with center in current position (i)
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+ if ($i + $k - 1 > $r) { // if right edge of current palindrome is righter than right edge of the previous rightest palindrome, renew l and r
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+ $l = $i - $k + 1;
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+ $r = $i + $k - 1;
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+ }
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+ }
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+
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+ /* Even subpalindromes
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+ a bit modified previous algorithm (for odd subpalindromes)
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+ */
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+ $l = 0;
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+ $r = -1;
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+ for ($i = 0; $i < $n; $i++) {
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+ $k = $i > $r ? 0 : min($even[$l + $r - $i + 1], $r - $i + 1);
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+ while ($i + $k < $n && $i - $k - 1 >= 0 && mb_substr($str, $i + $k, 1) == mb_substr($str, $i - $k - 1, 1)) {
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+ $k++;
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+ }
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+ $even[$i] = $k;
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+ if ($i + $k - 1 > $r) {
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+ $l = $i - $k;
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+ $r = $i + $k - 1;
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+ }
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+ }
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+
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+ return [$odd, $even];
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+ }
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+ }
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CrazyPhD
4 years ago