Weekly Challenge 244

Each week Mohammad S. Anwar sends out The Weekly Challenge, a chance for all of us to come up with solutions to two weekly tasks. My solutions are written in Python first, and then converted to Perl. It's a great way for us all to practice some coding.

Challenge, My solutions

Task 1: Count Smaller

Task

You are given an array of integers.

Write a script to calculate the number of integers smaller than the integer at each index.

My solution

This is a one-liner in Python

solution = [sum(1 for j in ints if j < i) for i in ints]

Breaking it down:

• for i in ints iterates through the supplied list, assigning each value to the variable i.
• sum(1...) will count the number of elements that satisfy the condition.
• for j in ints creates an inner loop, assigning each value to the variable 'j'.
• Finally j < i will only count the elements where the value in the inner loop is lower than the outer loop.

As Perl does not provide an easy way for double loops, I create a separate function to calculate the values less than a number, and then use the map function to iterate through each value.

sub less_than($i, $ints) {
    return scalar( grep { $_ < $i } @$ints );
}

my @solution = map { less_than( $_, \@ints ) } @ints;

Examples

$ ./ch-1.py 8 1 2 2 3
4, 0, 1, 1, 3

$ ./ch-1.py 6 5 4 8
2, 1, 0, 3

$ ./ch-1.py 2 2 2
0, 0, 0

Task 2: Group Hero

Task

You are given an array of integers representing the strength.

Write a script to return the sum of the powers of all possible combinations; power is defined as the square of the largest number in a sequence, multiplied by the smallest.

My solution

For this task, I create a function called calculate_power that returns the square of the largest number multiplied by the smallest number.

def calculate_power(numbers):
    min_int = min(numbers)
    max_int = max(numbers)
    return max_int ** 2 * min_int

In the main function, I create a loop called length which goes from 1 to the length of the supplied list. For each length, I compute all combinations. Thankfully Python has a combination function in itertools.

for length in range(1, len(ints)+1):
    power += sum(calculate_power(c) for c in combinations(ints, length))

Perl's combination function comes from the Algorithm::Combinatorics module.

foreach my $len ( 1 .. $#ints+1) {
    my $iter = combinations(\@ints, $len);
    while (my $c = $iter->next) {
        $power += calculate_power($c);
    }
}

Examples

$ ./ch-2.py 2 1 4
141