这是我获取所有可能性的代码:
$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>';
但是如果我想添加更多,那么我将不得不再添加一个循环。那么,我该如何使用递归呢?我努力,我努力,但我真的做不到。 请帮助并尽可能简单地发布示例。
谢谢。
最佳答案
这里有一个算法,
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;
}
我知道它在任何方面都不是有效的,但在小范围内使用应该不是问题
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。
为了简单的使用和输出:
var_dump(getCombinations(array("a","b","c","d"),2));
输出是
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)
要列出一个数组的所有子集,使用这个组合算法只需执行
$base =array("a","b","c","d");
for($i = 1; $i<=4 ;$i++){
$comb = getCombinations($base,$i);
foreach($comb as $c){
echo implode(",",$c)."<br />";
}
}
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
关于php递归获取所有可能的字符串,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4279722/