Loop Code Optimization

Question

How can I optimize the following code ,

I Need to run 3 sets of loops like this:

for($i=1;$i<=$count-1;$i++){    
  for($j=$i+1;$j<=$count;$j++){
  // do some query use $i and $j

  }
}
for($i=1;$i<=$count-2;$i++){
   for($j=$i+1;$j<=$count-1;$j++){   
     for($k=$j+1;$k<=$count;$k++){
       // do some query use $i and $j and $k
     }
  }
}
for($i=1;$i<=$count-3;$i++){
   for($j=$i+1;$j<=$count-2;$j++){   
      for($k=$j+1;$k<=$count-1;$k++){
     for($l=$k+1;$l<=$count;$l++){ 
       // do some query use $i and $j and $k and $l
       }
     }
  }
}

Is there a way to simplify the code, perhaps to connect the loops together ?

thanks !

Answer 1

The big problem is that the inner loops are run multiple times. You can get around this by checking i === 1 and j === 2 inside the loops and only running the appropriate code if true.

Answer 2

Micro-optimization: Use

++$i

rather than

$i++

and equivalent for $j++, $k++ and $l++

But what are you doing in these loops: it's entirely possible that your do some query (database?) could be changed to remove the loops completely... and that would be far more effective than any micro-optimisations

Answer 3

This should do it (untested):

for($i = 1; $i <= $count - 3; $i++) {
    for($j = $i + 1; $j <= $count; $j++) {
        // i,j query

        if($j > $count - 2) {
            continue;
        }

        for($k = $j + 1; $k <= $count; $k++) {
            // i,j,k query

            if($k > $count - 1) {
                continue;
            }

            for($l = $k + 1; $l <= $count; $l++) {
                // i,j,k,l query
            }
        }
    }
}

Note that the queries are no longer in their original order.

As it has been said, there's no way to optimize this further without knowing the queries you are running.