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