# Perl Weekly Challenge 91.

My solutions (task 1 and task 2) to the The Weekly Challenge - 091.

You are given a positive number \$N.

Write a script to count number and display as you read it.

Example 1:

``````Input: \$N = 1122234
Output: 21321314
``````

as we read “two 1 three 2 one 3 one 4”

Example 2:

``````Input: \$N = 2333445
Output: 12332415
``````

as we read “one 2 three 3 two 4 one 5”

Example 3:

``````Input: \$N = 12345
Output: 1112131415
``````

as we read “one 1 one 2 one 3 one 4 one 5”

This task is a straightforward run length encoding (RLE) of the digits of a number without the subleties of RLE. My solution is straightforward. First, some pragmas and packages.

``````# Perl weekly challenge 091
# Simple RLE encoding of a sequence of digits.
use warnings;
use strict;
use v5.10;
use List::Util qw(all);
use Scalar::Util::Numeric qw(isint);
``````

Take the arguments from the command line.

``````die "Usage ./ch-1.pl n0 n1 ... to codify numbers n0 n1 ..." unless @ARGV;
die "Only non-negative numbers allowed" unless all {isint \$_ == 1} @ARGV;
``````

For each digit, if repeated, increment its count, if not, print count of previous digit and initialize new count. Use a unique end marker to force printing of the last digit. The coding seems ambiguous for a large number of repetitions: 1213 means one 2 and one 3 or a hundred and twenty one 3’s? 101 means one 0 and a malformed string or ten 1’s? In order to avoid problems, I don’t encode more than 9 repetitions. Thus, 11111111111 is coded as nine 1’s and another two 1’s. The use of empty printable strings instead of uninitialized values, and a last non-digit marker, require string instead of numerical comparisons. I don’t know what should I do with leading zeroes, so I allow perl to remove them using int.

``````for my \$N(map {int \$_} @ARGV){
print "Input:\t\$N\nOutput:\t";
my \$current_digit=""; # Initialize to something printable
my \$current_count="";
foreach(split(//, \$N), "I'm not a digit"){ # digits and a unique stop marker
if(\$current_digit ne \$_  || \$current_count eq 9){ # string comparisons
print "\$current_count\$current_digit";
\$current_count=0;
\$current_digit=\$_;
}
++\$current_count;
}
say "\n";
}
``````

Example:

``````./ch-1.pl 1122234 2333445 12345 1111111111111111111 000 0000123
``````

Results:

``````Input:	1122234
Output:	21321314

Input:	2333445
Output:	12332415

Input:	12345
Output:	1112131415

Input:	1111111111111111111
Output:	919111

Input:	0
Output:	10

Input:	123
Output:	111213
``````

Code.

You are given an array of positive numbers @N, where value at each index determines how far you are allowed to jump further.

Write a script to decide if you can jump to the last index. Print 1 if you are able to reach the last index otherwise 0.

Example 1:

``````Input: @N = (1, 2, 1, 2)
Output: 1
``````

as we jump one place from index 0 and then two places from index 1 to reach the last index.

Example 2:

``````Input: @N = (2,1,1,0,2)
Output: 0
``````

it is impossible to reach the last index. as we jump two places from index 0 to reach index 2, followed by one place jump from index 2 to reach the index 3. once you reached the index 3, you can’t go any further because you can only jump 0 position further.

I solve this challenge by making a set of stepping stones working backwards from the last one. A stone is a stepping stone if from it we can reach another stepping stone[ 1 ].

First, the usual stuff and a couple of packages.

``````# Perl weekly challenge 091
# Test if you can reach last element of an array by succesive jumps of bounded lengths.

use strict;
use warnings;
use v5.10;
use List::Util qw(all);
use Scalar::Util::Numeric qw(isint);
``````

Check the arguments. Initialize the array taking the values from @ARGV. The goal is to reach position `\$#stones` from position `0`.

``````die "Usage: ./ch-2.pl s0 s1 s2...\n\t with sn maximum number of steps from stone n"
unless @ARGV;
die "Only non-negative numbers allowed" unless all {isint \$_ == 1} @ARGV;
my @stones=@ARGV;
``````

For all stones, check if you can reach from them any stepping stone and update resulting set accordingly. Print result. Since the problem is 1D, it is enough to reach the closest stepping stone.

``````my @stepping_stones;
push @stepping_stones, \$#stones;
foreach(reverse (0..\$#stones-1)){ # add stepping stones from right to left
unshift @stepping_stones, \$_ if \$stepping_stones <= \$_+\$stones[\$_];
}
say \$stepping_stones==0
?"1 Success\nPath: " . join "->", @stepping_stones
:"0 Failure";
``````

Example 1:

``````./ch-2.pl 1 2 1 2
``````

Results:

``````1 Success
Path: 0->1->2->3
``````

Example 2:

``````./ch-2.pl 2 1 1 0 2
``````

Results:

``````0 Failure
``````

Example 3:

``````./ch-2.pl 2 0 3 0 2 0 1
``````

Results:

``````1 Success
Path: 0->2->4->6
``````

Code.

# Footnotes

1 After seeing other answers (2020-12-21) I guess several participants took `@N` as an array of actual jump lengths, not of maximum allowed jumps. This makes the problem easier, but less interesting. Unfortunately, the examples are consistent with both interpretations.

Written on December 14, 2020