Php递归获得所有可能的字符串
这是我的代码来获得所有可能性:
$seq[1] = 'd';
$seq[2] = 'f';
$seq[3] = 'w';
$seq[4] = 's';
for($i = 1; $i < 5; $i++)
{
$s['length_1'][] = $seq[$i];
$c1++;
for($i2 = $i+1; $i2 < 5; $i2++)
{
$s['length_2'][] = $seq[$i].$seq[$i2];
$last = $seq[$i].$seq[$i2];
$c2++;
for($i3 = $i2+1; $i3 < 5; $i3++)
{
$s['length_3'][] = $last.$seq[$i3];
$last = $last.$seq[$i3];
$c3++;
for($i4 = $i3+1; $i4 < 5; $i4++)
{
$s['length_4'][] = $last.$seq[$i4];
$c4++;
}
}
}
}
for($i = 0; $i < $c1; $i++)
echo $s['length_1'][$i].'<br>';
for($i = 0; $i < $c2; $i++)
echo $s['length_2'][$i].'<br>';
for($i = 0; $i < $c3; $i++)
echo $s['length_3'][$i].'<br>';
for($i = 0; $i < $c4; $i++)
echo $s['length_4'][$i].'<br>';
但如果我想添加更多,那么我将不得不添加一个循环。 那么,我怎样才能做到递归? 我尝试,我尝试,但我真的不能这样做。 请尽可能简单地帮助并发布示例。
谢谢。
这是一个简单的算法。 从1到2 count(数组)-1迭代。 在每次迭代中,如果循环计数器的二进制表示中的第j位等于1,则在组合中包含第j个元素。
由于PHP需要能够将2count(array)计算为整数,因此这可能永远不会超过PHP_INT_MAX
。 在64位PHP安装中,阵列不能超过62个元素,因为262保持在PHP_INT_MAX
以下,而263超过它。
编辑:这个计算所有可能的组合,而不是排列(即'abc'='cba')。 它通过以二进制表示原始数组并且从0向整数组的二进制表示“向上计数”,从而有效地构建每个可能的唯一组合列表。
$a = array('a', 'b', 'c', 'd');
$len = count($a);
$list = array();
for($i = 1; $i < (1 << $len); $i++) {
$c = '';
for($j = 0; $j < $len; $j++)
if($i & (1 << $j))
$c .= $a[$j];
$list[] = $c;
}
print_r($list);
一种算法在这里,
function getCombinations($base,$n){
$baselen = count($base);
if($baselen == 0){
return;
}
if($n == 1){
$return = array();
foreach($base as $b){
$return[] = array($b);
}
return $return;
}else{
//get one level lower combinations
$oneLevelLower = getCombinations($base,$n-1);
//for every one level lower combinations add one element to them that the last element of a combination is preceeded by the element which follows it in base array if there is none, does not add
$newCombs = array();
foreach($oneLevelLower as $oll){
$lastEl = $oll[$n-2];
$found = false;
foreach($base as $key => $b){
if($b == $lastEl){
$found = true;
continue;
//last element found
}
if($found == true){
//add to combinations with last element
if($key < $baselen){
$tmp = $oll;
$newCombination = array_slice($tmp,0);
$newCombination[]=$b;
$newCombs[] = array_slice($newCombination,0);
}
}
}
}
}
return $newCombs;
}
我知道这不是有效的,但是使用小套不应该是一个问题
第一个基本参数是一个数组,其中包含生成组合时要考虑的元素。
简单的使用和输出:
var_dump(getCombinations(array("a","b","c","d"),2));
并输出
array
0 =>
array
0 => string 'a' (length=1)
1 => string 'b' (length=1)
1 =>
array
0 => string 'a' (length=1)
1 => string 'c' (length=1)
2 =>
array
0 => string 'a' (length=1)
1 => string 'd' (length=1)
3 =>
array
0 => string 'b' (length=1)
1 => string 'c' (length=1)
4 =>
array
0 => string 'b' (length=1)
1 => string 'd' (length=1)
5 =>
array
0 => string 'c' (length=1)
1 => string 'd' (length=1)
要列出数组的所有子集,只需执行使用此组合算法即可
$base =array("a","b","c","d");
for($i = 1; $i<=4 ;$i++){
$comb = getCombinations($base,$i);
foreach($comb as $c){
echo implode(",",$c)."<br />";
}
}
和输出是
a
b
c
d
a,b
a,c
a,d
b,c
b,d
c,d
a,b,c
a,b,d
a,c,d
b,c,d
a,b,c,d
这里是:
<?php
function combinations($text,$space)
{
// $text is a variable which will contain all the characters/words of which we want to make all the possible combinations
// Let's make an array which will contain all the characters
$characters=explode(",", $text);
$x=count($characters);
$comb = fact($x);
// In this loop we will be creating all the possible combinations of the positions that are there in the array $characters
for ($y=1; $y<= $comb; $y++)
{
$ken = $y-1;
$f = 1;
$a = array();
for($iaz=1; $iaz<=$x; $iaz++)
{
$a[$iaz] = $iaz;
$f = $f*$iaz;
}
for($iaz=1; $iaz<=$x-1; $iaz++)
{
$f = $f/($x+1-$iaz);
$selnum = $iaz+$ken/$f;
$temp = $a[$selnum];
for($jin=$selnum; $jin>=$iaz+1; $jin--)
{
$a[$jin] = $a[$jin-1];
}
$a[$iaz] = $temp;
$ken = $ken%$f;
}
$t=1;
// Let’s start creating a word combination: we have all the necessary positions
$newtext="";
// Here is the while loop that creates the word combination
while ($t<=$x)
{
$newtext.=$characters[$a[$t]-1]."$space";
$t++;
}
$combinations[] = $newtext ;
}
return $combinations;
}
function fact($a){
if ($a==0) return 1;
else return $fact = $a * fact($a-1);
}
$a = combinations("d,f,w,s","");
foreach ($a as $v) {
echo "$v"."n";
}
?>
输出:
dfws
dfsw
dwfs
dwsf
dsfw
dswf
fdws
fdsw
fwds
fwsd
fsdw
fswd
wdfs
wdsf
wfds
wfsd
wsdf
wsfd
sdfw
sdwf
sfdw
sfwd
swdf
swfd
另外,请阅读本文;
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