07 June 2024

Challenge 272

Defang the Snake Fixated at the Score

• Task 1: Defang IP Address
• Task 2: String Score

Task 1: Defang IP Address

Submitted by: Mohammad Sajid Anwar

---

You are given a valid IPv4 address.

Write a script to return the defanged version of the given IP address.

A defanged IP address replaces every period “.” with “[.]”.

Example 1

Input: $ip = "1.1.1.1"
Output: "1[.]1[.]1[.]1"

Example 2

Input: $ip = "255.101.1.0"
Output: "255[.]101[.]1[.]0"

---

Solution

Just putting square brackets around dots seems to be too easy for a task. So at least let us verify the input string as a valid IPv4 address.

But there is another interesting aspect: We may substitute the regular expression [.] with the string [.]. Utilizing proper delimiters and a little fantasy, we arrive at an expression with a pair of snake eyes fixated on us. Shouldn’t we better defang that snake?

use strict;
use warnings;
use Regexp::Common 'net';

sub defang {
    return /^$RE{net}{IPv4}$/ &&

    s([.])([.])gr

    for shift;
}

See the full solution to task 1.

Task 2: String Score

Submitted by: Mohammad Sajid Anwar

---

Write a script to return the score of the given string.

The score of a string is defined as the sum of the absolute difference between the ASCII values of adjacent characters.

Example 1

Input: $str = "hello"
Output: 13

ASCII values of characters:
h = 104
e = 101
l = 108
l = 108
o = 111

Score => |104 - 101| + |101 - 108| + |108 - 108| + |108 - 111|
      => 3 + 7 + 0 + 3
      => 13

Example 2

Input: "perl"
Output: 30

ASCII values of characters:
p = 112
e = 101
r = 114
l = 108

Score => |112 - 101| + |101 - 114| + |114 - 108|
      => 11 + 13 + 6
      => 30

Example 3

Input: "raku"
Output: 37

ASCII values of characters:
r = 114
a = 97
k = 107
u = 117

Score => |114 - 97| + |97 - 107| + |107 - 117|
      => 17 + 10 + 10
      => 37

---

Solution

The subclass PDL::Char of PDL comes handy, when dealing with fixed sized arrays of ASCII characters. By converting them back to a true numeric type, computations on the strings may be performed easily.

use strict;
use warnings;
use PDL;
use PDL::NiceSlice;
use PDL::Char;

sub score {
    my $s = PDL::Char->new(shift);
    sum abs long($s(0:-2)) - long($s(1:-1));
}

See the full solution to task 2.

---

If you have a question about this post or if you like to comment on it, feel free to open an issue in my github repository.