[tips]转换parent-child二元关系为关系链

/*
       将
        $relationArr  = array(
            3=>array(1,3),
            5=>array(3,5),
            7=>array(6,7),
            10=>array(9,10),
            23=>array(20,23),
            700=>array(5,700),
            1203=>array(10,1203),
        );
      转化成

        $finalArr = array(
            3=>array(1,3,5,700),
            7=>array(6,7),
            10=>array(9,10,1203),
            23=>array(20,23),
        );

     复杂度O(n^2),关系链越长，越趋近O(n)
    n 为 $relationArr 数组元素数量

*/

        $finalArr = array();
        foreach($relationArr as $k => $v)
        {
            if(empty($finalArr))
            {//first element in $finalArr
                $finalArr[$k] = $v;
                continue;
            }

            $bIsFind = false;
            foreach($finalArr as $k1 => $v1)
            {
                $index = count($v1) - 1;
                if( $v1[$index] == $v[0] )
                {//match
                    $finalArr[$k1][1+$index] = $v[1];
                    $bIsFind = true;
                    break;
                }
            }

            if(!$bIsFind)
            {//new first-failed flow Instance
                $finalArr[$k] = $v;
            }
        }