How to iterate a loop of array circularly in php? - php

Question

Suppose i have a number let's say 5. Now lets assume that there are 5 members. Now each member started to count 1 to 2. Those member who get 2nd number leaves and then again count start from the next member. so at last in this scenario the 3rd member stays at last.
So i tried to implement like this. First of assign members as array $v.
for($i=1 ; $i<=5 ; $i++)
{
$v[] = $i;
}
$v1 = array_flip($v);
for($i=0 ; $i<=5 ; $i += 2 )
{
unset($v1[$i]);
}
echo "<pre>";
print_r($v1);
output
Array
(
[1] => 0
[3] => 2
[5] => 4
)
Now i want to count the numbers from key 5(5th member) to again 1(1st member) and so on.
so at last key 3(3rd member) left.
I want to print the last member that left.
How can i achieve this?
I you can't understand then look at this
Survival Strategy

Answer 1

Here's an Object-Oriented solution with an easy-to-follow reduce method and multiple examples.
class CountByTwoArrayReducer {
public function __construct($array) {
$this->array = $array;
$this->size = count($array);
}
public function reduce() {
$this->initialize();
while($this->hasMultipleItems()) {
$this->next();
$this->removeCurrentItem();
$this->next();
}
return $this->finalItem();
}
protected function initialize() {
$this->current = 1;
$this->removed = array();
$this->remaining = $this->size;
}
protected function hasMultipleItems() {
return ($this->remaining > 1);
}
protected function next($start = null) {
$next = ($start === null) ? $this->current : $start;
do {
$next++;
} while(isset($this->removed[$next]));
if($next > $this->size)
$this->next(0);
else
$this->current = $next;
}
protected function removeCurrentItem() {
$this->removed[$this->current] = 1;
$this->remaining--;
}
protected function finalItem() {
return $this->array[$this->current - 1];
}
}
$examples = array(
array('A', 'B', 'C', 'D', 'E'),
range(1, 100),
range(1, 1000),
range(1, 10000)
);
foreach($examples as $example) {
$start = microtime(true);
$reducer = new CountByTwoArrayReducer($example);
$result = $reducer->reduce();
$time = microtime(true) - $start;
echo "Found {$result} in {$time} seconds.\n";
}

Answer 2

This will remove every other item from the array until there is only a single item left.
$members = range(1, 5);
$i = 0;
while(count($members) > 1) {
$i++;
if($i == count($members)) $i = 0;
unset($members[$i]);
$members = array_values($members);
if($i == count($members)) $i = 0;
}
echo $members[0];

Answer 3

Hmm, I can recommend two functions:
http://php.net/manual/en/function.array-keys.php
This would re-index you array, with indexes: 0, 1, 2
http://php.net/manual/en/control-structures.foreach.php
With this you can go through any array by:
foreach($v1 as $key=>$value) { ...select maximum, etc. ... }

Answer 4

<?php
function build_thieves($thieves)
{
return range(1, $thieves);
}
function kill_thief(&$cave)
{
if(sizeof($cave)==1)
{
$thief=array_slice($cave, 0, 1);
echo $thief.' survived';
return false;
}
$thief=array_slice($cave, 0, 1);
array_push($cave, $thief);
$thief=array_slice($cave, 0, 1);
echo $thief.' killed';
return true;
}
$cave=build_thieves(5);
$got_data=true;
while($got_data)
{
$got_data=kill_thief($cave);
}
Adjusted to every 2nd, not every 3rd. And starting from 1 not 0

Answer 5

This answer is a bit more complex, but it is much more efficient. It doesn't create an array of items and then remove them. It starts with a value (e.g. 1) and calculates the next item that has not been removed yet. Then, it flags it as removed. If you actually have an array of items, the index of the final item will be $current - 1. The example below uses values 1 through 10,000. On my machine, it takes just over 0.05 seconds.
define('SIZE', 10000);
/**
* Helper function to return the next value
*/
function get_next($current, &$removed) {
$next = $current;
do {
$next++;
} while(isset($removed[$next]));
return ($next > SIZE) ? get_next(0, $removed) : $next;
}
$current = 1;
$removed = array();
$remaining = SIZE;
$start_time = microtime(true);
while($remaining > 1) {
$current = get_next($current, $removed);
$removed[$current] = 1;
$remaining = SIZE - count($removed);
$current = get_next($current, $removed);
}
$total_time = microtime(true) - $start_time;
echo "Processed " . SIZE . " items\n";
echo "Winning item: {$current}\n";
echo "Total time: {$total_time} seconds\n";