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The problem is explained here

https://stackoverflow.com/questions/47912489/combinations-without-duplicates-using-php

Please reply here no in stackoverflow , thanks.

## 2 Solutions

This is a rather interesting problem so I decided to have a go at it despite the small pay.

The big problem that makes you run out of memory is that you're generating all the combinations explicitly (and rather inefficiently at that) into an array. Filtering that array after generating it will not solve that problem.

Instead, you should use a generator, which will allow you to generate each combination one after the other, and use them one by one.

Here, I ported the example implementation of the `itertools.combinations`

generator from the Python docs:

```
<?php
function combinations($elems, $k) {
$n = sizeof($elems);
if ($k > $n) {
return;
}
$map_fn = function($i) use ($elems) {
return $elems[$i];
};
$elems = array_values($elems);
$indices = range(0, $k-1);
yield array_map($map_fn, $indices);
while (true) {
$broke = false;
foreach (range($k-1, 0, -1) as $i) {
if ($indices[$i] != $i + $n - $k) {
$broke = true;
break;
}
}
if (!$broke) {
return;
}
$indices[$i] += 1;
if ($k-1 >= $i+1) {
foreach (range($i+1, $k-1) as $j) {
$indices[$j] = $indices[$j-1] + 1;
}
}
yield array_map($map_fn, $indices);
}
}
$numeri = "01.02.03.04.05.06.07.08.09.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30";
$numeri_ar = array_map('intval', explode(".", $numeri));
$numeri_ar = array_unique($numeri_ar);
$archivio = array();
foreach (file("archive.txt") as $line) {
$assoc = array();
foreach (explode(".", trim($line)) as $n) {
$assoc[intval($n)] = 1;
}
array_push($archivio, $assoc);
if (sizeof($archivio) >= 200) {
break;
}
}
foreach (combinations($numeri_ar, 5) as $comb) {
$okay = true;
foreach ($archivio as $arch_comb) {
$found = 0;
foreach ($comb as $c) {
if (array_key_exists($c, $arch_comb)) {
if (++$found >= 3) {
$okay = false;
break;
}
}
}
if (!$okay) {
break;
}
}
if ($okay) {
printf("%s\n", join(".", array_map('strval', $comb)));
}
}
?>
```

The output is printed line-by-line to stdout using the `n.n.n.n.n`

format, which can be dumped into a file using `php script.php > output.txt`

. Otherwise, you can also change line 69 to append `$comb`

to an array instead.

200 lines are taken from `archive.txt`

. `$numeri`

is set to [01-30] as per the Stack Overflow question. For testing, k is set to 5, which doesn't take too long to complete.

At 30 choose 5, the number of combinations is 142'506, but after filtering, it drops to 123'447 valid combinations. That's only a ~15% reduction, but with a bigger k, I suppose it could get reduced more. However, I'm not sure if it would really drop to only a few thousand combinations considering 30 choose 18 is 86'493'225.

It would be more efficient to embed the filtering logic into the generator, but I've already stretched that $10 far too much.

Hi there,

ok here is my solution for your bounty, as we discussed:

```
function subcombi($arr, $arr_size, $count)
{
$combi_arr = array();
if ($count > 1) {
for ($i = $count - 1; $i < $arr_size; $i=$i+1) {
$highest_index_elem_arr = array($i => $arr[$i]);
foreach (subcombi($arr, $i, $count - 1) as $subcombi_arr)
{
$combi_arr[] = $subcombi_arr + $highest_index_elem_arr;
}
}
} else {
for ($i = $count - 1; $i < $arr_size; $i=$i+1) {
$combi_arr[] = array($i => $arr[$i]);
}
}
return $combi_arr;
}
function combinations($arr, $count)
{
if ( !(0 <= $count && $count <= count($arr))) {
return false;
}
return $count ? subcombi($arr, count($arr), $count) : array();
}
$numeri="55.77.03.04.30.06.47.71";
$numeri_ar=explode(".",$numeri);
$numeri_ar=array_unique($numeri_ar);
for ($combx = 2; $combx < 6; $combx++)
{
$combi_ar = combinations($numeri_ar, $combx);
}
//full cominations array is ready
//print_r($combi_ar);
//get archivio content
$archivio = file_get_contents('archivio.txt');
$archivio_ar = explode("\n",$archivio);
//save only the first 30 rows
$archivio_ar = array_slice($archivio_ar, 0, 30, true);
//echo $archivio;
print_r($archivio_ar);
$wantedCombinations = [];
//now we will test for each combination
foreach($combi_ar as $combination){
//we make a test for each line
foreach($archivio_ar as $dataset_row){
$dataset_row_ar = explode(".",$dataset_row);
$intersect_ar = array_intersect($combination, $dataset_row_ar);
//we count intersection, if less than 3, we save it
if( count($intersect_ar) < 3 ){
$wantedCombinations[] = $combination; break;
}
}
}
//echo $wantedCombinations;
print_r($wantedCombinations);
```

i have completed your code, and commented it, the idea is simple, read the archive content, and check intersections, between the two combinations. in the intersection count is less than 3, so we save it as you require. otherwise, we skip it. you can change the condition for further inquiries ;)

hope this fits your case ;)

`archive.txt`

is 71.29.47.30.63 which has 3 numbers in common (71, 47, 30).