请教一个二维数组元素组合的算法
$arr = array( array('a','b','c'), array('c','f'), array('g','z'), array('x','y'));//$arr子集元素长度可能会多一些//将$arr的子集元素与$arr其他子集元素两两组合或者三三四四组合//子集array('a','b','c')中的元素不需要组合//两两组合$newarr = array( array('a','c'), array('a','f'), array('b','c'), array('b','f'), array('c','c'), array('c','f'), ……)//三三组合$newarr = array( array('a','c','g'), array('a','f','g'), array('b','c','g'), array('b','f','g'), array('c','c','g'), array('c','f','g'), ……)//四四组合$newarr = array( array('a','c','g','x'), array('a','f','g','x'), array('b','c','g','x'), array('b','f','g','x'), array('c','c','g','x'), array('c','f','g','x'), ……)
用一个函数可以实现吗?
//$arr:原始数组,$cNum:组合长度function getCombination($arr,$cNum){ ……}
回复讨论(解决方案)
你把一个 Combination(n 取 m 的组合)和一个 Descartes(笛卡尔积)函数揉和在一起就可以了
其实并不需要只写成一个函数,写成一个反而失去了普遍性
我一开始也是想到,先取符合长度的数组,再求笛卡尔积
先用递归,再求积,最后合并数组?
如果是这样,那么
function getCombination($arr, $cNum) { $res = array(); foreach( Combination($arr, $cNum) as $item) { $res = array_merge($res, Descartes($item)); } return $res;}
两个函数的可能写法是
function Combination( $arr, $num=0) { $arr = array_values($arr); $len = count($arr); if($num <= 0 || $num > $len) $num = $len; $res = array(); for($i=1,$n=pow(2, $len); $i<$n; ++$i) { $tmp = str_pad(base_convert($i, 10, 2), $len, '0', STR_PAD_LEFT); $t = array(); for($j=0; $j<$len; ++$j) { if($tmp{$j} == '1') { $t[] = $arr[$j]; } } if(count($t) == $num) $res[] = $t; } return $res;}function Descartes($d) { $r = array_pop($d); while($d) { $t = array(); $s = array_pop($d); if(! is_array($s)) $s = array($s); foreach($s as $x) { foreach($r as $y) $t[] = array_merge(array($x), is_array($y) ? $y : array($y)); } $r = $t; } return $r;}
常用的算法都应写成函数,形成代码库。在需要时调用,不必每次都写
常用的算法都应写成函数,形成代码库。在需要时调用,不必每次都写
谢谢版主,睡觉的,马上就看您写的,学习学习再学习
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