DEV Community: Daisy Rono

Data Structure and Algorithms 102: Deep Dive into Data Structure and Algorithms

Daisy Rono — Sun, 26 Jun 2022 06:36:41 +0000

Alice and Bob each created one problem for HackerRank. A reviewer rates the two challenges, awarding points on a scale from 1 to 100 for three categories: problem clarity, originality, and difficulty.

The rating for Alice's challenge is the triplet a = (a[0], a[1], a[2]), and the rating for Bob's challenge is the triplet b = (b[0], b[1], b[2]).

The task is to find their comparison points by comparing a[0] with b[0], a[1] with b[1], and a[2] with b[2].

If a[i] > b[i], then Alice is awarded 1 point.
If a[i] < b[i], then Bob is awarded 1 point.
If a[i] = b[i], then neither person receives a point.

Comparison points is the total points a person earned.

Given a and b, determine their respective comparison points.

Example

a = [1, 2, 3]
b = [3, 2, 1]

For elements 0, Bob is awarded a point because a[0] .
For the equal elements a[1] and b[1], no points are earned.
Finally, for elements 2, a[2] > b[2] so Alice receives a point.

The return array is [1, 1] with Alice's score first and Bob's second.

Function Description

Complete the function compareTriplets in the editor below.

compareTriplets has the following parameter(s):

int a[3]: Alice's challenge rating
int b[3]: Bob's challenge rating

Return

int[2]: Alice's score is in the first position, and Bob's score is in the second.

Input Format

The first line contains 3 space-separated integers, a[0], a[1], and a[2], the respective values in triplet a.
The second line contains 3 space-separated integers, b[0], b[1], and b[2], the respective values in triplet b.

Constraints

1 ≤ a[i] ≤ 100
1 ≤ b[i] ≤ 100

Sample Input 0

5 6 7
3 6 10

Sample Output 0

1 1

Explanation 0

In this example:

a = (a[0],a[1],a[2])=(5,6,7)
b = (b[0],b[1],b[2])=(3,6,10)

Now, let's compare each individual score:

a[0] > b[0], so Alice receives point.
a[1] = b[1], so nobody receives a point.
a[2] < b[2], so Bob receives point.

Alice's comparison score is 1, and Bob's comparison score is 1. Thus, we return the array [1,1].

Sample Input 1

17 28 30
99 16 8

Sample Output 1

2 1

Explanation 1

Comparing the 0#th elements 17<99, so Bob receives a point.
Comparing the 1#st and 2#nd elements, 28>16 and 30>18 so Alice receives two points. The return array is [2,1].

The solution in PHP:

function compareTriplets($a, $b) {
    // Write your code here
    $aAward = 0;
    $bAward = 0;

    for ($i=0;$i<3;$i++){
        if($a[$i]>$b[$i]){
            $aAward +=1;
        }elseif($a[$i]<$b[$i]){
            $bAward +=1;
        }
    }

return array($aAward,$bAward);
}

In Python3:

def compareTriplets(a, b):
    # Write your code here
    aAward = 0
    bAward = 0

    for i in range(0,3):
        if(a[i]>b[i]):
            aAward += 1
        if (a[i]<b[i]):
            bAward += 1

    return [aAward,bAward]

In Kotlin:

fun compareTriplets(a: Array<Int>, b: Array<Int>): Array<Int> {

    var aAward =0 
    var bAward= 0 
    // Write your code here

    for (i in 0..2){
        if(a[i]>b[i]){
            aAward += 1
        }
        if(a[i]<b[i]){
            bAward +=1
        } 
    }
return arrayOf(aAward,bAward);
}

Splitting a 3x3 matrix into all possible 2x2 matrices using PHP

Daisy Rono — Sat, 18 Jun 2022 12:01:08 +0000

Creating the 3x3 matrix

To create a 3x3 matrix, begin with an array

$a = array(array(1,5,7),array(7,3,5),array(2,6,9));
$rows = count($a);
$cols = count($a[0]);

for ($k = 0; $k < $rows; $k++){
    for ($j = 0; $j < $cols; $j++){
        echo ($a[$k][$j]."  ");
    }
    echo ("<br>");
}

This will result in

1 5 7
7 3 5
2 6 9

Getting 2x2 matrices

There are 4 possible 2x2 matrices that could be derived from the 3x3 matrix above.

Begin with row index zero and column index zero and reduce the number of rows and columns by one. (since its a 3x3 matrix we wish to reduce to a 2x2, the row and column both reduce by one)
To create another matrix, Increment either the row by one. Repeat this step with the column, this time holding the row constant.

The first 2x2 matrix is begins at k = 0 and j = 0. However, the arrays are reduced by one from both ends like seen in the code:

for ($k = 0; $k < $rows-1; $k++){
    for ($j = 0; $j < $cols-1; $j++){
        echo ($a[$k][$j]." ");
    }
    echo ("<br>");
}

The output of this is:

1 5
7 3

The maximum and minimum values of this matrix are 7 and 1 respectively.

The second 2x2 matrix has the row starting at k=0 and ending at k < row-1 but the column starts at j =1 and ends at j < cols as shown below:

for ($k = 0; $k < $rows-1; $k++){
    for ($j = 1; $j < $cols; $j++){
        echo ($a[$k][$j]." ");
    }
    echo ("<br>");
}

The output of this is:

5 7
3 5

The maximum and minimum values of this matrix are 7 and 3 respectively.

Here, the rows start at k =1 while the columns start at j =0.

for ($k = 1; $k < $rows; $k++){
    for ($j = 0; $j < $cols-1; $j++){
        echo ($a[$k][$j]." ");
    }
    echo ("<br>");
}

The output of this is:

7 3
2 6

The maximum and minimum values of this matrix are 7 and 2 respectively.

Now, both rows and columns start at 1.

for ($k = 1; $k < $rows; $k++){
    for ($j = 1; $j < $cols; $j++){
        echo ($a[$k][$j]." ");
    }
    echo ("<br>");
}

The output of this is:

3 5
6 9

The maximum and minimum values of this matrix are 9 and 3 respectively.

The Minimum and Maximum values Matrices

To merging the minimum values to form other matrix of minimum values using arrays, use

#minimum value
echo "<br>";
$b =array(array(1,3),array(2,3));
$rows_b = count($b);
$cols_b = count($b[0]);
for ($i = 0; $i < $rows_b; $i++){
    for ($l = 0; $l < $cols_b; $l++){
        echo ($b[$i][$l]."  ");
    }
    echo ("<br>");
}

This results to a matrix of the form

1 3
2 3

The same concept is applied to maximum values using

$c =array(array(7,7),array(7,9));
$rows_c = count($c);
$cols_c = count($c[0]);
for ($m = 0; $m < $rows_c; $m++){
    for ($n = 0; $n < $cols_c; $n++){
        echo ($c[$m][$n]."  ");
    }
    echo ("<br>");
}

resulting in the 2x2 matrix below.

7 7
7 9

Data Structures 101: Introduction to Data Structures and Algorithms.

Daisy Rono — Thu, 16 Jun 2022 08:25:57 +0000

Problem

Given an array of integers, find the sum of its elements.
For example, if the array ar=[1,2,3],1+2+3=6,so return 6.

Function Description

Complete the simpleArraySum function in the editor below. It must return the sum of the array elements as an integer.

simpleArraySum has the following parameter(s):

ar: an array of integers

Input Format

The first line contains an integer, n, denoting the size of the array.
The second line contains n space-separated integers representing the array's elements.

Constraints
0 < n, ar[i] < 1000

Output Format

Print the sum of the array's elements as a single integer.

Sample Input

6
1 2 3 4 10 11

Sample Output

Explanation

We print the sum of the array's elements:
1+2+3+4+10+11=31

Solution

Here, three approaches are used to solve this problem.

1. Foreach
This approach does not require the the size of the array hence the most likely loop to be used for this problem.

function simpleArraySum($ar) {
    // Write your code here
    $sum = 0;
    foreach($ar as $value){
        $sum += $value;
    }
        return $sum;
}

2. For Loop
The size of the array and the sum of the array are initialized before using for loop. The indices of the arrays to be summed are incremented by one to move to the next item in the array.

function simpleArraySum($ar) {
    $size = count($ar);
    $sum = 0;

    for($i=0 ; $i < $size; $i++){
      $sum += $ar[$i];
    }

    return $sum;
}

3. While Loop

This is the same as for loop but the operation stops when the condition $i < count($ar) is no longer true.

function simpleArraySum($ar){
    $sum = 0;
    $i = 0;
    while($i < count($ar)){
        $sum += $ar[$i];
        $i++;
    }
    return $sum;

}

The output of all three approaches is