Optimization of Unnecessary Loop Iterations in PHP

In the following code, a certain programmer checks if the array contains the number 3:

php<?php
  $arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
  
  $exists = false;
  foreach ($arr as $elem) {
    if ($elem == 3) {
      $exists = true;
    }
  }
  
  var_dump($exists);
?>

What's wrong with their solution? It seems like no unnecessary operations are performed in the loop. The problem, however, is that after it's determined that the number 3 is in the array - the loop still continues to run until the end of the array.

The most inefficient scenario would be if the number 3 is found somewhere at the beginning of the array, and the array itself has a length of, say, 1000 elements. That would result in a thousand useless extra loop iterations! Not optimal.

Let's optimize the code by stopping the loop in time:

php<?php
  $arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
  
  $exists = false;
  foreach ($arr as $elem) {
    if ($elem == 3) {
      $exists = true;
      break;
    }
  }
  
  var_dump($exists);
?>

Задание 1

The following code calculates how many array elements need to be added for the sum to become greater than 10. Perform optimization:

php<?php
  $arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
  $sum = 0;
  $i = 1;
  
  foreach ($arr as $elem) {
    $sum += $elem;
    
    if ($sum <= 10) {
      $i++;
    }
  }
  
  echo $i;
?>

Задание 2

The following code outputs even numbers from a given range. Perform optimization:

php<?php
  for ($i = 0; $i <= 100; $i++) {
    if ($i % 2 === 0) {
      echo $i;
    }
  }
?>

Задание 3

The following code outputs numbers divisible by both 2 and 3. Perform optimization:

php<?php
  for ($i = 0; $i <= 100; $i++) {
    if ($i % 2 === 0 and $i % 3 === 0) {
      echo $i;
    }
  }
?>