Get repeating strings in PHP array

getRepeatingString.php

<?php
/**
* ===========================================
* Compare strings and return repeating string
* ===========================================
*
* EXAMPLE:
*
* $strings = array(
*	"oh this is repeating string number one",
*	"and this is repeating string too",
*	"this is repeating string also",
*);
*
* echo getRepeatingString($strings); // "this is repeating string"
*
* @author Jan Zatloukal / rotten77.cz
* @param array $strings
* @return string $compare
*/
function getRepeatingString($strings) {
	foreach($strings as $key=>$string) {
		$strings[$key] = mb_strtolower($string, "utf-8");
	}
	 foreach($strings as $key=>$string) {
	 	
	 	$compareStartA = -1;
	 	$compareStartB = -1;

	 		$strA = ($key==0 ? explode(" ", $strings[0]) : $compare);
	 		$compare = array();
	 		$strB = explode(" ", $string);

		 	foreach($strA as $keyA=>$valA) {
		 		foreach($strB as $keyB=>$valB) {
		 			if($valA==$valB) {
		 					$compareStartA = ($compareStartA>=0 ? $compareStartA : $keyA);
		 					$compareStartB = ($compareStartB>=0 ? $compareStartB : $keyB);
		 				}
		 		}
		 	}

		 	$idx=0;
		 	foreach($strA as $keyA=>$valA) {
		 		if($strA>=$compareStartA) {
		 			if(isset($strB[$compareStartB+$idx]) && $valA==$strB[$compareStartB+$idx]) {
		 				$compare[] = $valA;
		 				$idx++;
		 			}
		 			

		 		}

		 	}
	 }

	 return implode(" ", $compare);
 }