how to compare the elemnts of an array [closed] - php

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Given a non-empty array, return true if there is a place to split the array so that the sum of the numbers on one side is equal to the sum of the numbers on the other side.

Answer 1

Break the problem up into smaller problems.
The array we will be using is:
$array = [1, 2, 3, 4, 5];
First thing first:
Understand the problem
In order to compare the left side with the right side you need to split the array until the sums of both sides are equal, or until there are no more items to sum.
Visually that would look something like this:
• ••••
•• •••
••• ••
•••• •
Problem: Can the array be split into two parts?
It is always a good idea to find out if what you are trying to do is even possible, or if doing it even makes sense.
With this problem we need at least 2 items in the array in order to split it into two parts. So, if the array has fewer than 2 items then we can safely return false and call it a day:
if (count($array) < 2) {
return false;
}
Problem: How to go through the array
The array needs to be split after each item in the array. So, we need to go through the array item by item.
| • | • | • | • | • |
0 1 2 3 4 5
We only need to split the array at 1, 2, 3 and 4. In other words, we should start after the first item and stop before the last item:
$length = count($array);
for ($i = 1; $i < $length; $i++) {
echo "Split after {$i}\n";
}
Problem: How to get the left/right side from the array
Getting the left and right side is a simple matter of extracting them from the array.
$left = array_slice($array, 0, $i);
$right = array_slice($array, $i);
If you put that into the loop and output it you will get something like this:
1 | 2 3 4 5
1 2 | 3 4 5
1 2 3 | 4 5
1 2 3 4 | 5
Problem: Sum and compare
PHP has a array_sum() function that sums values in arrays:
if (array_sum($left) === array_sum($right)) {
return true;
}
One solution
function my_func($array) {
if (count($array) < 2) {
return false;
}
$length = count($array);
for ($i = 1; $i < $length; $i++) {
$left = array_slice($array, 0, $i);
$right = array_slice($array, $i);
if (array_sum($left) === array_sum($right)) {
return true;
}
}
return false;
}
var_dump(my_func([1, 2, 3, 4, 5])); // false
var_dump(my_func([7, 1, 2, 3, 1])); // true: 7 = (1 + 2 + 3 + 1)

Answer 2

(Assuming our input array contains numbers.)
Start by adding all the elements of the array to each other (total sum). Then iterate through the array and add each element to each other as we go (cumulative sum). If during our iteration we discover that our cumulative sum is equal to half the total sum, we know that the other members of the array will also add up to the half sum, and hence the array can be split.
<?php
function can_split(array $numbers) {
$total_sum = array_sum($numbers);
$half_sum = $total_sum / 2;
$cumulative_sum = 0;
foreach($numbers as $num) {
$cumulative_sum += $num;
if($cumulative_sum == $half_sum)
return true;
}
}
var_dump(can_split(array(1))); // null
var_dump(can_split(array(1,2,3))); // true
var_dump(can_split(array(10,1,9))); // true
var_dump(can_split(array(3,5,9))); // null
var_dump(can_split(array(1.5,2,3,3,3.5))); // true