Array Manipulation HackerRank in PHP

Question

I try to resolve this exercise in Hacker Rank:

Starting with a 1-indexed array of zeros and a list of operations, for each operation add a value to each the array element between two given indices, inclusive. Once all operations have been performed, return the maximum value in the array.

Example:

n = 10
queries = [[1,5,3],[4,8,7],[6,9,1]]

Queries are interpreted as follows:

Add the values of k between the indices a and b inclusive:

index->  1 2 3  4  5 6 7 8 9 10
        [0,0,0, 0, 0,0,0,0,0, 0]
        [3,3,3, 3, 3,0,0,0,0, 0]
        [3,3,3,10,10,7,7,7,0, 0]
        [3,3,3,10,10,8,8,8,1, 0]

The largest value is after all operations are performed.
Function Description

Complete the function arrayManipulation in the editor below.

arrayManipulation has the following parameters:

int n - the number of elements in the array int queries[q][3] - a two dimensional array of queries where each queries[i] contains three integers, a, b, and k. Returns

int - the maximum value in the resultant array Input Format

The first line contains two space-separated integers and , the size of the array and the number of operations. Each of the next lines contains three space-separated integers , and , the left index, right index and summand.
I used this code:

function arrayManipulation($n, $queries) {
    for($i = 1; $i <= $n; $i++){
        $a[$i] = 0;
    }
    foreach($queries as $index => $query){   
            $e = $query[0];
            $p = $query[1];
            $value = $query[2];
            for($b = $e; $b <= $p; $b++){
                $a[$b] += $value;
            }
    }
    return max($a);
}

All work except for biggest test case (Runtime Error), how i can improve that?
Seems like very easy task but i can't solve it.

The logic i have used:

Create an array with index = $n (size of array)
Start to foreach $queries and create a tmp variable with:
- $e min of range
- $p max of range
- $value the value need for the sum
Use for-loop for sum value into array $a base to index from min and max
return max of $a

Your second link ends up with a 401 (unauthorized) error. Can you include the relevant information in the question itself instead of linking to an external resource? — rickdenhaan, Aug 06 '21 at 14:00
Was a biggest test case like 20000 row, i can't add here because will exceed the max size of post. — Simone Rossaini, Aug 06 '21 at 14:04
Please share more details. What is "this problem"? What kind of input breaks the algorithm? What have you tried to resolve the problem? — Nico Haase, Aug 06 '21 at 14:14
As your code does not print anything related to "Runtime Error", you need to share more details — Nico Haase, Aug 06 '21 at 14:15
Hacker rank "test" have a maximum time, seems like my script go runtime. which details you need more ? The only way is use test case, but i can't post it here — Simone Rossaini, Aug 06 '21 at 14:16
In general, problems like this require you to find a clever solution that's not O(n^2), so that you don't exceed the time limit on large inputs. In this case, what you need to do is turn the list of operations into an array containing the total amount to add to each array element. — Barmar, Aug 06 '21 at 14:25
Isn't that already the case? `$queries` contains the range and value to add. how could I enclose it any other way? — Simone Rossaini, Aug 06 '21 at 14:40
@ShivamSharma i really don't understand. You can be more specific — Simone Rossaini, Aug 06 '21 at 14:46
[Already a solution](https://stackoverflow.com/a/56327605/8494462) is posted using Prefix sum. — Shivam Sharma, Aug 06 '21 at 14:58
Does this answer your question? [Array Manipulation : HackerRank Questions : JAVA](https://stackoverflow.com/questions/56249944/array-manipulation-hackerrank-questions-java) — Shivam Sharma, Aug 06 '21 at 14:58
Logic remains same everywhere... Such questions are for improving DS algo, logical ability and problem solving skills. :) — Shivam Sharma, Aug 07 '21 at 10:45
Logic but the situation in not the same :D I don't know java(who used ? ) I prefer php and js ecc — Simone Rossaini, Aug 07 '21 at 11:58

trckster · Accepted Answer · 2021-08-06T15:09:06.183

I found the way to solve this problem in O(m * log(m)). It passes all test cases.

Look at my solution:

function arrayManipulation($n, $queries)
{
    $arr = [];

    foreach ($queries as $query) {
        $start = $query[0] - 1;
        $end = $query[1];
        $value = $query[2];

        $arr[$start] = ($arr[$start] ?? 0) + $value;

        if ($end < $n) {
            $arr[$end] = ($arr[$end] ?? 0) - $value;
        }
    }

    ksort($arr);

    $answer = 0;
    $currentSum = 0;

    foreach ($arr as $change) {
        $currentSum += $change;
        $answer = max($answer, $currentSum);
    }

    return $answer;
}

At first we should avoid using array of size n.
Then we construct array of value changes $arr, not of real values (like you've done).
And finally we just run through the resulting array and emulate real value for every iteration. And remember max value, of course. This will be our answer.

Array Manipulation HackerRank in PHP

1 Answers1