Finding value between ranges without going through the entire ranges - php

Question

I want to grant bonuses to my players based on how many friends they have.
I have breakpoints (for example 0, 1, 5, 10, 25)
For 0 friends he gets 0 bonus.
For 1 friend he gets 1000, for 5 or above 2000 etc...
What I do right now is this:
public function getFriendsBonusByFriendsAmount($amount)
{
switch (true) {
case ($amount < 1):
return 0;
case ($amount < 5):
return 1000;
case ($amount < 10):
return 2000;
case ($amount < 25):
return 3000;
case ($amount >= 25):
return 5000;
}
}
I'm looking for a different way to find the bonus without foreach/switch
Perhaps think of an array or arrays that I could play with?
$bonusBreakpoints = [
0 => 0,
1 => 1000,
5 => 2000,
10 => 3000,
25 => 5000
]
Or perhaps two arrays with respective indexs?
I thought of a way to do it but it's a memory waste:
$bonusPerFriends = [
0 => 0,
1 => 1000,
2 => 1000,
3 => 1000,
4 => 1000,
5 => 2000,
6 => 2000,
...
25 => 5000
]
I rather not to use that way.

Answer 1

Well, sometimes foreach/switch will be the best solution :)
/**
* Calculates bonus based on how many
* friends the player have from predefined breakpoints
**/
function getBonus($friends) {
$bonuses = [0, 1000, 2000, 3000, 5000];
$stops = [[PHP_INT_MIN, 0], [1, 4], [5, 14], [15, 24], [25, PHP_INT_MAX]];
// replace the stops by bonus if match, otherwise return empty - O(n)
$bonus = array_map(function ($stop, $bonus) use ($friends) {
if ($friends >= $stop[0] && $friends <= $stop[1]) {
return $bonus;
}
}, $stops, $bonuses);
// clean up the array from empty values - O(n)
$bonus = array_filter($bonus , 'is_numeric');
// from array(3 => 3000) to 3000 - O(1)
return array_pop($bonus);
}
results:
echo getBonus(0).PHP_EOL; // 0
echo getBonus(4).PHP_EOL; // 1000
echo getBonus(12).PHP_EOL; // 2000
echo getBonus(20).PHP_EOL; // 3000
echo getBonus(39).PHP_EOL; // 5000
P.S. $bonuses and $stops here must be equal length.

Answer 2

#andrey-mischenko 's answer is technically right, but does not solve the problem without foreach, as you said in your question. (Edit: answer was removed) Try this:
$bonusBreakpoints = [
0 => 0,
1 => 1000,
5 => 2000,
10 => 3000,
25 => 5000
];
$justTheKeys = array_keys($bonusBreakpoints);
public function getFriendsBonusByFriendsAmount($amount)
{
$bonus = array_reduce($justTheKeys, function($carryOver, $item) use ($amount)
{
if ($amount >= $item) return $bonusBreakpoints($item);
return $carryOver;
}
return $bonus;
}
(I'm aware that this is not what array_reduce is originally intended for. I understood the question as a mind-game. Like "find creative ways to solve this problem apart from the obvious ones, like loops or switches." If I had to code this for work, I'd probabely use a loop, too. :) )

Answer 3

After reading the answer and more research I concludes that binary search is my best option.
The data should look somewhat like this:
$bonuses = [
[ 'min' => 0, 'max' => 0, 'amount' => 0 ]
[ 'min' => 1, 'max' => 4, 'amount' => 1000 ]
[ 'min' => 5, 'max' => 14, 'amount' => 2000 ]
...
[ 'min' => 25, 'max' => PHP_INT_MAX, 'amount' => 5000 ]
]
You start at the count($bonuses)/2 and from there check whether you are below the min, is so goes halfway, otherwise check if you are above max, and go halfway there. else... just return the bonus coz you are between the right range.
Since most of my users don't have any friends or more than 25 I would probably check the first and last cell first.