<?php$arr = array('a','b','c','d');$result = array();$t = getCombinationToString($arr, 1);print_r($t);$t = getCombinationToString($arr, 2);$t2 = getunique($t);print_r($t2);$t = getCombinationToString($arr, 3);$t2 = getunique($t);print_r($t2);$t = getCombinationToString($arr, 4);$t2 = getunique($t);print_r($t2);function getunique($t){	$t2 = array();	//print_r($t);	for($i=0;$i<count($t);$i++){		$count_list = array_count_values($t[$i]);		$flag = 1;		foreach($count_list as $ck=>$cv){			if($cv>1){				$flag = 0;				break;			}		}		if($flag){			sort($t[$i]);			$flag2 = 1;			if($t2){				foreach($t2 as $t2k=>$t2v){					if($t[$i]==$t2v){						$flag2 = 0;						break;					}				}			}			if($flag2){				$t2[] = $t[$i];			}		}	}	return $t2;}function getCombinationToString($arr, $m) {	if ($m ==1) {	 return $arr;	}	$result = array();		$tmpArr = $arr;	unset($tmpArr[0]);	for($i=0;$i<count($arr);$i++) {		$s = $arr[$i];		$ret = getCombinationToString(array_values($tmpArr), ($m-1), $result);				foreach($ret as $row) {			//$result[] = $s . $row;			$temp = array();			$temp[] = $s;			if(is_array($row)){				$temp = array_merge($temp,$row);			}else{				$temp[] = $row;			}			sort($temp);			$result[] = $temp;		}	} return $result;}?>